Method and apparatus for encoding/decoding images using adaptive motion vector resolution

ABSTRACT

The present disclosure relates to a method and apparatus for improving the encoding efficiency by adaptively changing the resolution of the motion vector in the inter prediction encoding and inter prediction decoding of a video. The apparatus includes: a predicted motion vector calculator for calculating a predicted motion vector of a current block to be encoded using motion vectors of one or more surrounding blocks; and a skip mode encoder for encoding a result of performing a prediction of the current block and information indicating that the current block is a skip block when the predicted motion vector satisfies a skip condition, wherein at least one motion vector among the motion vectors of the surrounding blocks and the motion vector of the current block has a resolution different from resolutions of the other motion vectors.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/847,364 filed on Apr. 13, 2020, which is a continuation ofU.S. patent application Ser. No. 15/895,912 filed on Feb. 13, 2018,which is a continuation of U.S. patent application Ser. No. 13/391,568filed Apr. 28, 2012, which is the National Phase application ofInternational Application No. PCT/KR2010/005571, filed Aug. 21, 2010,which is based on and claims priority to Korean Patent Application No.10-2009-0077452 filed on Aug. 21, 2009 and Korean Patent Application No.1 0-201 0-0081 099 filed on Aug. 20, 2010. The disclosures of theabove-listed applications are hereby incorporated by reference herein intheir entireties.

TECHNICAL FIELD

The present disclosure relates to a method and an apparatus forencoding/decoding images using adaptive motion vector resolution. Moreparticularly, the present disclosure relates to a method and anapparatus for improving the encoding efficiency by adaptively changingthe resolution of the motion vector in the inter prediction encoding andinter prediction decoding of a video.

BACKGROUND ART

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Encoding of data for a video generally involves an intra predictionencoding and an inter prediction encoding. The intra prediction encodingand the inter prediction encoding are effective methods capable ofreducing the correlation existing between multiple pieces of data, whichare widely used in various data compressions. Especially, in the interprediction encoding, since a motion vector of a current block determinedthrough estimation of the motion of the current block to be currentlyencoded has a close relation with motion vectors of the surroundingblocks, a predicted motion vector (PMV) for the motion vector of thecurrent block is first calculated from the motion vectors of thesurrounding blocks and only a differential motion vector (DMV) for thePMV is encoded instead of encoding the motion vector of the currentblock itself, so as to considerably reduce the quantity of bits to beencoded and thus improve the encoding efficiency.

That is, in the case of performing the inter prediction encoding, anencoder encodes and transmits only a DMV corresponding to a differentialvalue between the current motion vector and a PMV determined throughestimation of the motion of the current block from a reference frame,which has been reconstructed through previous encoding and decoding. Adecoder reconstructs the current motion vector by adding the PMV and theDMV transmitted based on a prediction of the motion vector of thecurrent block using the motion vectors of the surrounding blockspreviously decoded.

Further, at the time of performing the inter prediction encoding, theresolution may be enhanced en bloc through interpolation of thereference frame, and a DMV corresponding to a differential value betweenthe current motion vector and a PMV determined through estimation of themotion of the current block may then be encoded and transmitted. In thisevent, the enhancement of the resolution of a reference video (i.e. thevideo of the reference frame) enables a more exact inter prediction andthus reduces the quantity of bits generated by the encoding of theresidual signal between the original video and a predicted video.However, the enhancement of the resolution of the reference video alsocauses an enhancement of the resolution of the motion vector, whichincreases the quantity of bits generated by the encoding of the DMV. Incontrast, although a decrease of the resolution of the reference videoincreases the quantity of bits generated by the encoding of the residualsignal, it decreases the resolution of the motion vector, resulting inthe corresponding decrease of the quantity of bits generated by encodingof the DMV.

As described above, since the conventional inter prediction encodinguses motion vectors of the same resolution obtained by interpolating allvideo encoding units, such as blocks, slices, and pictures, of a videowith the same resolution, it is difficult for the conventional interprediction encoding to achieve an efficient encoding, which may degradethe compression efficiency.

DISCLOSURE Technical Problem

Therefore, the present disclosure has been made in view of the abovementioned problems to improve the encoding efficiency by adaptivelychanging the resolution of the motion vector in the inter predictionencoding and inter prediction decoding of a video.

Technical Solution

An aspect of the present disclosure provides an apparatus forencoding/decoding a video, the apparatus including: a video encoder forcalculating a predicted motion vector of a current block to be encodedby using motion vectors of one or more surrounding blocks, and encodinga result of performing a prediction of the current block and informationindicating that the current block is a skip block when the predictedmotion vector satisfies a skip condition; and a video decoder fordecoding information indicating that a current block to be decoded is askip block, calculating a predicted motion vector of the current blockto be decoded by using motion vectors of one or more surrounding blocks,selecting the calculated predicted motion vector as a motion vector ofthe current block to be decoded, and decoding the current block in askip mode by using the motion vector of the current block, wherein atleast one motion vector among the motion vectors of the surroundingblocks and the motion vector of the current block has a resolutiondifferent from resolutions of the other motion vectors.

Another aspect of the present disclosure provides an apparatus forencoding a video in a skip mode, the apparatus including: a predictedmotion vector calculator for calculating a predicted motion vector of acurrent block to be encoded by using motion vectors of one or moresurrounding blocks; and a skip mode encoder for encoding a result ofprediction of the current block and information indicating that thecurrent block is a skip block when the predicted motion vector satisfiesa skip condition, wherein at least one motion vector among the motionvectors of the surrounding blocks and the motion vector of the currentblock has a resolution different from resolutions of the other motionvectors.

Yet another aspect of the present disclosure provides an apparatus forencoding a video in a skip mode, the apparatus including: a predictedmotion vector calculator for calculating a predicted motion vector of acurrent block to be encoded by using motion vectors of one or moresurrounding blocks; a skip mode encoder for encoding a result ofperforming a prediction of the current block and information indicatingthat the current block is a skip block when the predicted motion vectorsatisfies a skip condition; and a resolution encoder for encodinginformation indicating a resolution of a motion vector of the currentblock.

Yet another aspect of the present disclosure provides an apparatus fordecoding a video, the apparatus including: a skip information extractorfor decoding information indicating that a current block to be decodedis a skip block; a predicted motion vector calculator for obtaining apredicted motion vector of the current block to be decoded by usingmotion vectors of one or more surrounding blocks; and a skip blockdecoder for selecting the predicted motion vector as a motion vector ofthe current block and decoding the current block in a skip mode by usingthe motion vector of the current block, wherein at least one motionvector among the motion vectors of the surrounding blocks and the motionvector of the current block has a resolution different from resolutionsof the other motion vectors.

Yet another aspect of the present disclosure provides an apparatus fordecoding a video in a skip mode, the apparatus including: a skipinformation extractor for decoding information indicating that a currentblock to be decoded is a skip block; a resolution decoder for decodinginformation indicating a resolution of a motion vector; a predictedmotion vector calculator for obtaining a predicted motion vector of thecurrent block to be decoded by using motion vectors of one or moresurrounding blocks and the information indicating the resolution of themotion vector; and a skip block decoder for selecting the calculatedpredicted motion vector as a motion vector of the current block to bedecoded and decoding the current block in the skip mode by using themotion vector of the current block.

Yet another aspect of the present disclosure provides a method forencoding/decoding a video, the method including: encoding a video bycalculating a predicted motion vector of a current block to be encodedby using motion vectors of one or more surrounding blocks, and encodinga result of performing a prediction of the current block and informationindicating that the current block is a skip block when the predictedmotion vector satisfies a skip condition; and decoding a video bydecoding information indicating that a current block to be decoded is askip block, calculating a predicted motion vector of the current blockto be decoded by using motion vectors of one or more surrounding blocks,selecting the predicted motion vector as a motion vector of the currentblock to be decoded, and decoding the current block in a skip mode byusing the motion vector of the current block, wherein at least onemotion vector among the motion vectors of the surrounding blocks and themotion vector of the current block has a resolution different fromresolutions of the other motion vectors.

Yet another aspect of the present disclosure provides a method forencoding a video in a skip mode, the method including: calculating apredicted motion vector of a current block to be encoded by using motionvectors of one or more surrounding blocks; and encoding a skip mode byencoding a result of performing a prediction of the current block andinformation indicating that the current block is a skip block when thepredicted motion vector satisfies a skip condition, wherein at least onemotion vector among the motion vectors of the surrounding blocks and themotion vector of the current block has a resolution different fromresolutions of the other motion vectors.

Yet another aspect of the present disclosure provides a method forencoding a video in a skip mode, the method including: calculating apredicted motion vector of a current block to be encoded by using motionvectors of one or more surrounding blocks; encoding a skip mode byencoding a result of performing a prediction of the current block andinformation indicating that the current block is a skip block when thepredicted motion vector satisfies a skip condition; and encoding aresolution by encoding information indicating a resolution of a motionvector of the current block.

Yet another aspect of the present disclosure provides a method fordecoding a video in a skip mode, the method including: extracting skipinformation by decoding information indicating that a current block tobe decoded is a skip block; calculating a predicted motion vector of thecurrent block to be decoded by using motion vectors of one or moresurrounding blocks; and decoding a skip block by selecting the predictedmotion vector as a motion vector of the current block to be decoded anddecoding the current block in the skip mode by using the motion vectorof the current block, wherein at least one motion vector among themotion vectors of the surrounding blocks and the motion vector of thecurrent block has a resolution different from resolutions of the othermotion vectors.

Yet another aspect of the present disclosure provides a method fordecoding a video in a skip mode, the method including: extracting skipinformation by decoding information indicating that a current block tobe decoded is a skip block; decoding a resolution by decodinginformation indicating a resolution of a motion vector; calculating apredicted motion vector of the current block to be decoded by usingmotion vectors of one or more surrounding blocks and the informationindicating the resolution of the motion vector; and decoding a skipblock by selecting the predicted motion vector as a motion vector of thecurrent block and decoding the current block in the skip mode by usingthe motion vector of the current block.

Advantageous Effects

According to the present disclosure as described above, a video can beencoded efficiently through an inter prediction encoding of the videowhile adaptively changing the resolution of the motion vector in theunit of a predetermined area.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a video encoding apparatus,

FIG. 2 is an exemplary diagram for illustrating the process ofinterpolating a reference picture,

FIG. 3 is an exemplary diagram for illustrating the process ofdetermining a predicted motion vector,

FIG. 4 shows an example of truncated unary codes wherein a maximum valueT thereof is 10,

FIG. 5 shows an example of the 0-th, first, and second order Exp-Golombcodes,

FIG. 6 shows an example of the Concatenated Truncated Unary/K-th OrderExp-Golomb Code wherein the maximum value T is 9 and K is 3,

FIG. 7 shows an example of a sequence of Zigzag scanning,

FIG. 8 is a schematic block diagram of a video decoding apparatus,

FIG. 9 is a block diagram illustrating a video encoding apparatusaccording to the first aspect of the present disclosure,

FIGS. 10A to 10C are exemplary diagrams for illustrating motion vectorresolutions hierarchically expressed by a Quadtree structure accordingto an aspect of the present disclosure,

FIG. 11 illustrates a hierarchically expressed result of encoded motionvector resolutions in a Quadtree structure according to an aspect of thepresent disclosure,

FIG. 12 illustrates motion vector resolutions of areas determinedaccording to an aspect of the present disclosure,

FIG. 13 illustrates an example of motion vector resolutionhierarchically expressed in a tag tree structure according to an aspectof the present disclosure,

FIG. 14 illustrates a result of the encoding of the motion vectorresolutions hierarchically expressed in a tag tree structure accordingto an aspect of the present disclosure,

FIG. 15 illustrates an example of a process for determining a motionvector resolution by using surrounding pixels of an area according to anaspect of the present disclosure,

FIG. 16 is a view for illustrating the process of predicting a predictedmotion vector according to an aspect of the present disclosure,

FIG. 17 is a flowchart for describing a method for encoding a video byusing an adaptive motion vector resolution according to an aspect of thepresent disclosure,

FIG. 18 is a schematic block diagram illustrating a video decodingapparatus using an adaptive motion vector according to an aspect of thepresent disclosure,

FIG. 19 is a flowchart of a method for decoding a video by using anadaptive motion vector resolution according to an aspect of the presentdisclosure,

FIG. 20 illustrates another scheme of dividing a node into lower layersaccording to an aspect of the present disclosure,

FIG. 21 illustrates an example of a bit string allocated to each ofsymbols depending on the motion vector resolutions according to anaspect of the present disclosure,

FIG. 22 illustrates optimum motion vectors of a current block andsurrounding blocks in order to describe a process of determining aresolution of a motion vector,

FIG. 23 illustrates a table showing conversion formulas according to themotion vector resolution,

FIG. 24 illustrates a table showing the resolutions of motion vectors ofsurrounding blocks converted based on block X to be currently encoded,

FIG. 25 illustrates a code number table of a differential motion vectoraccording to the motion vector resolutions,

FIG. 26 illustrates optimum motion vectors of a current block andsurrounding blocks in order to describe a process of determining aresolution of a differential motion vector by the resolution determiner,

FIG. 27 illustrates a code number table of differential motion vectorsaccording to the differential motion vector resolutions,

FIG. 28 illustrates a motion vector of the current block and a referencemotion vector of surrounding blocks,

FIG. 29 illustrates a code number table of a differential referencemotion vector according to the differential reference motion vectorresolution,

FIG. 30 illustrates an example of indexing and encoding a referencepicture based on a distance between a current picture and a referencepicture,

FIG. 31 is a table illustrating an example of reference picture indexesaccording to reference picture numbers and resolutions,

FIG. 32 is a schematic block diagram illustrating a video encodingapparatus 3200 using an adaptive motion vector according to the secondaspect of the present disclosure,

FIG. 33 illustrates resolution identification flags in the case in whichthe appointed resolutions are ½ and ¼,

FIG. 34 illustrates current block and its surrounding blocks,

FIG. 35 illustrates a context model according to the conditions,

FIG. 36 illustrates resolution identification flags in the case in whichthe appointed resolutions are ½, ¼, and ⅛,

FIG. 37 illustrates a context model according to the conditions,

FIGS. 38 and 39 illustrate examples of adaptability degrees according todistances between the current picture and reference pictures,

FIG. 40 illustrates an example of storing different reference pictureindex numbers according to predetermined resolution sets,

FIG. 41 illustrates an example of a structure for encoding of referencepictures,

FIG. 42 illustrates an example of resolution sets of reference pictureswhen the resolution sets are appointed to ½ and ¼,

FIG. 43 illustrates an example of a resolution of a current block andresolutions of surrounding blocks,

FIG. 44 illustrates another example of a resolution of a current blockand resolutions of surrounding blocks,

FIG. 45 illustrates resolution identification flags according toresolutions,

FIG. 46 illustrates an example of the resolution of the current blockand the resolutions of surrounding blocks,

FIG. 47 is a flowchart illustrating a video encoding method using anadaptive motion vector resolution according to the second aspect of thepresent disclosure,

FIG. 48 is a schematic block diagram illustrating a video decodingapparatus using an adaptive motion vector according to the second aspectof the present disclosure,

FIG. 49 illustrates an example of surrounding motion vectors of currentblock,

FIG. 50 illustrates an example of converted values of surrounding motionvectors according to the current resolution,

FIG. 51 is a flowchart illustrating a video decoding method using anadaptive motion vector resolution according to the second aspect of thepresent disclosure,

FIG. 52 is a block diagram illustrating a video encoding apparatus 5200using an adaptive motion vector according to the third aspect of thepresent disclosure, and

FIG. 53 is a block diagram illustrating a video decoding apparatus usingan adaptive motion vector according to the third aspect of the presentdisclosure.

MODE FOR INVENTION

Hereinafter, aspects of the present disclosure will be described indetail with reference to the accompanying drawings. In the followingdescription, the same elements will be designated by the same referencenumerals although they are shown in different drawings. Further, in thefollowing description of the present disclosure, a detailed descriptionof known functions and configurations incorporated herein will beomitted when it may make the subject matter of the present disclosurerather unclear.

Additionally, in describing the components of the present disclosure,there may be terms used like first, second, A, B, (a), and (b). Theseare solely for the purpose of differentiating one component from theother but not to imply or suggest the substances, order or sequence ofthe components. If a component were described as ‘connected’, ‘coupled’,or ‘linked’ to another component, they may mean the components are notonly directly ‘connected’, ‘coupled’, or ‘linked’ but also areindirectly ‘connected’, ‘coupled’, or ‘linked’ via a third component.

A video encoding apparatus or video decoding apparatus describedhereinafter may be a personal computer or PC, notebook or laptopcomputer, personal digital assistant or PDA, portable multimedia playeror PMP, PlayStation Portable or PSP, or mobile communication terminal,smart phone or such devices, and represent a variety of apparatusesequipped with, for example, a communication device such as a modem forcarrying out communication between various devices or wired/wirelesscommunication networks, a memory for storing various programs forencoding videos and related data, and a microprocessor for executing theprograms to effect operations and controls.

In addition, the video encoded into a bitstream by the video encodingapparatus may be transmitted in real time or non-real-time to the videodecoding apparatus for decoding the same where it is reconstructed andreproduced into the video after being transmitted via a wired/wirelesscommunication network including the Internet, a short range wirelesscommunication network, a wireless LAN network, a WiBro (WirelessBroadband) also known as WiMax network, and a mobile communicationnetwork or a communication interface such as cable or USB (universalserial bus).

In addition, although the video encoding apparatus and the videodecoding apparatus may be equipped with the functions of performing theinter prediction as well as the intra prediction, which lacks a directcorrelation with the aspects of the present disclosure, a detaileddescription thereof will not be provided to avoid any confusions.

A video typically includes a series of pictures each of which is dividedinto predetermined areas, such as blocks. When each picture is dividedinto blocks, each of the blocks is classified into an intra block or aninter block depending on the method of classification. The intra blockmeans the block that is encoded through an intra prediction coding whichis within a current picture where the current encoding is performed forgenerating a predicted block by predicting a current block using pixelsof a reconstructed block that underwent previous encoding and decodingand then encoding the differential value of the predicted block from thepixels of the current block. The inter block means the block that isencoded through an inter prediction coding which generates the predictedblock by predicting the current block in the current picture throughreferencing one or more past pictures or future pictures to predict thecurrent block in the current picture and then encoding the differentialvalue of the predicted block from the current block. Here, the picturethat is referenced in encoding or decoding the current picture is calleda reference picture.

The following description discusses apparatuses for encoding anddecoding a video by blocks through examples shown in FIGS. 1 to 8 ,wherein the block may be a macroblock having a size of M×N or a subblockhaving a size of O×P. However, the encoding or decoding of a video byblocks is just an example and a video may be encoded or decoded not onlyby standardized areas, such as blocks, but also by non-standardizedareas.

FIG. 1 is a schematic diagram showing a video encoding apparatus.

The video encoding apparatus 100 may include a predictor 110, asubtracter 120, a transformer 130, a quantizer 140, an encoder 150, aninverse quantizer 160, an inverse transformer 170, an adder 180, and amemory 190.

The predictor 110 generates a predicted block by performing intraprediction on the current block. In other words, in response to an inputof a block to be currently encoded, i.e. a current block, the predictor110 predicts original pixel values of pixels of the current block byusing motion vectors of the current block determined through motionestimation, to generate and output the predicted block having predictedpixel values.

The subtracter 120 generates a residual block of the current block bysubtracting the predicted block from the current block. Here, theoutputted residual block includes a residual signal which has a valueobtained by subtracting the predicted pixel value of the predicted blockfrom the original pixel value of the current block.

The transformer 130 generates a transformed block by transforming theresidual block. Specifically, the transformer 130 transforms a residualsignal of the residual block outputted from the subtracter 120 into thefrequency domain to generate and output the transformed block having atransform coefficient. Here, the method used for transforming theresidual signal into the frequency domain may be the discrete cosinetransform (DCT) based transform or Hadamard transform among variousother unlimited transforming techniques available from improving andmodifying the DCT transform or the like, whereby the residual signal istransformed into the frequency domain and into the transformcoefficient.

The quantizer 140 quantizes the transformed block to generate atransformed and quantized block. Specifically, the quantizer 140quantizes the transform coefficient of the transformed block outputtedfrom the transformer 130 to generate and output the transformed andquantized block having a quantized transform coefficient. Here, thequantizing method used may be the dead zone uniform thresholdquantization (DZUTQ) or the quantization weighted matrix among theirvarious improvement options.

The encoder 150 encodes the transformed and quantized block to output abitstream. In particular, the encoder 150 encodes a frequencycoefficient string resulted from scanning in the zig-zag scanning orother various scanning methods with respect to the quantized transformcoefficient of the transformed and quantized block outputted from thequantizer 140, by using various encoding techniques such as the entropyencoding, and generates and outputs the bitstream encompassingadditional information needed to decode the involved block such asprediction mode information, quantization parameter, motion vector, etc.

The inverse quantizer 160 carries out the inverse process ofquantization with respect to the transformed and quantized block.Specifically, the inverse quantizer 160 inversely quantizes and outputsthe quantized transform coefficients of the transformed and quantizedblock outputted from the quantizer 140.

The inverse transformer 170 carries out the inverse process oftransformation with respect to the transformed and inversely quantizedblock. Specifically, the inverse transformer 170 inversely transformsthe inversely quantized transform coefficients from the inversequantizer 160 to reconstruct the residual block having the reconstructedresidual coefficients.

The adder 180 adds the inversely transformed and reconstructed residualblock from the inverse transformer 170 to the predicted block from thepredictor 110 to reconstruct the current block. The reconstructedcurrent block is stored in the memory 190 and may be accumulated byblocks or by pictures and then transferred in units of pictures to thepredictor 110 for possible use in predicting other blocks including thenext block or the next picture.

Meanwhile, the predictor 110 determines the motion vector of the currentblock by estimating the motion of the current block by using thereference picture stored in the memory 190, and may perform the motionestimation after enhancing the resolution of the reference picture byinterpolating the reference picture stored in the memory 190.

FIG. 2 is a view for illustrating the process of interpolating areference picture.

FIG. 2 shows pixels of the reference picture stored in the memory 190and pixels interpolated by using sub-pixels. Sub-pixels a˜s can begenerated by interpolating previously reconstructed pixels A˜U of thereference picture by using an interpolation filter, and the sub-pixelsa˜s interpolated between the previously reconstructed pixels canincrease the resolution of the reference picture fourfold or more.

The motion estimation refers to a process of finding a part of aninterpolated reference picture which is most similar to the currentblock and outputting a block of the part and a motion vector indicatingthe part. A predicted block found in this process is subtracted from thecurrent block by the subtracter 120, so as to produce a residual blockhaving a residual signal. Further, the motion vector is encoded by theencoder 150.

When encoding the motion vector, the encoder 150 may predict the motionvector of the current block by using motion vectors of blocks adjacentto the current block and may encode the motion vector by using thepredicted motion vector.

FIG. 3 is a view for illustrating the process of determining a predictedmotion vector.

Referring to FIG. 3 , based on an assumption that the current block isX, a motion vector of an adjacent block A located at the left side ofthe current block is MV_A (x component: MVx_A, y component: MVy_A), amotion vector of an adjacent block B located at the upper side of thecurrent block is MV_B (x component: MVx_B, y component: MVy_B), and amotion vector of an adjacent block C located at the right upper side ofthe current block is MV_C (x component: MVx_C, y component: MVy_C), eachcomponent of the predicted motion vector MV_pred_X (x component:MVx_pred_X, y component: MVy_pred_X) of the current block X may bedetermined as a median value of each component of the motion vector ofan adjacent block of the current block as shown in Equation 1 below.Meanwhile, the method of predicting a motion vector according to thepresent disclosure is not limited to the method introduced herein.MVx_pred_X=median(MVx_A, MVx_B, MVx_C)MVy_pred_X=median(MVy_A, MVy_B, MVy_C)   Equation 1

The encoder 150 may encode a differential vector having a differentialvalue between a motion vector and a predicted motion vector. Variousentropy encoding schemes, such as a Universal Variable Length Coding(UVLC) scheme and a Context-Adaptive Binary Arithmetic Coding (CABAC)scheme, may be used for encoding the differential vector. Meanwhile, inthe present disclosure, the encoding method by the encoder 150 is notlimited to the method described herein.

In the case of encoding the differential vector by using the UVLC, thedifferential vector may be encoded by using the K-th order Exp-Golombcode. In this event, K may have a value of “0” or another value. Theprefix of the K-th order Exp-Golomb code has a truncated unary codecorresponding to l(x)=└log₂(x/2^(k)+1)┘, and a suffix thereof may beexpressed by a binary-coded bit stream of a value of x+2^(k)(1-2^(l(x)))having a length of k+l(x).

FIG. 4 shows an example of truncated unary codes wherein a maximum valueT thereof is 10, and FIG. 5 shows an example of the 0-th, first, andsecond order Exp-Golomb codes.

Further, when the differential vector is encoded using the CABAC, thedifferential vector may be encoded using code bits of the ConcatenatedTruncated Unary/K-th Order Exp-Golomb Code.

In the Concatenated Truncated Unary/K-th Order Exp-Golomb Code, themaximum value T is 9 and K may be 3. FIG. 6 shows an example of theConcatenated Truncated Unary/K-th Order Exp-Golomb Code wherein themaximum value T is 9 and K is 3.

FIG. 7 shows an example of a sequence of Zigzag scanning.

The quantized frequency coefficients quantized by the quantizer 140 maybe scanned and encoded into a quantized frequency coefficient string bythe encoder 150. Block type quantized frequency coefficients may bescanned according to not only the zigzag sequence as shown in FIG. 7 butalso various other sequences.

FIG. 8 is a schematic block diagram of a video decoding apparatus.

The video decoding apparatus 800 may include a decoder 810, an inversequantizer 820, an inverse transformer 830, an adder 840, a predictor850, and a memory 860.

The decoder 810 decodes a bitstream to extract the transformed andquantized block. Specifically, the decoder 810 decodes a bit stringextracted from the bitstream received and inversely scans the result toreconstruct the transformed and quantized block having a quantizedtransform coefficient. At the same time, the decoder 810 uses the sameencoding technique like the entropy encoding as used by the encoder 150of the video encoding apparatus 100 to perform the reconstruction.

Further, the decoder 810 may extract and decode an encoded differentialvector from the bitstream to reconstruct the differential vector, andmay predict a motion vector of the current block and then add thepredicted motion vector to the reconstructed differential vector toreconstruct the motion vector of the current block.

The inverse quantizer 820 inversely quantizes the transformed andquantized block. Specifically, the inverse quantizer 820 inverselyquantizes the quantized transform coefficient of the transformed andquantized block from the decoder 810. At this time, the inversequantizer 820 in its operation performs a reversal of the quantizationtechnique used in the quantizer 140 of the video encoding apparatus 100.

The inverse transformer 830 inversely transforms the transformed andinversely quantized block to reconstruct the residual block.Specifically, the inverse transformer 830 reconstructs the inverselyquantized transform coefficient of the transformed and inverselyquantized block from the inverse quantizer 820, wherein the inversetransformer 830 in its operation performs a reversal of the transformtechnique used in the transformer 130 of the video encoding apparatus100.

The predictor 850 generates a predicted block by predicting the currentblock by using the reconstructed motion vector of the current blockextracted and decoded from the bitstream.

The adder 840 adds the reconstructed residual block to the predictedblock to reconstruct the current block. Specifically, the adder 840 addsa reconstructed residual signal of the reconstructed residual blockoutputted from the inverse transformer 830 to the predicted pixel valuesof the predicted block outputted from the predictor 850 to calculate thereconstructed pixel values of the current block, thereby reconstructingthe current block.

The current block reconstructed by the adder 840 is stored in the memory860. The current blocks may be stored as reference pictures by blocks orby pictures for use in the prediction of a next block by the predictor850.

As described above with reference to FIGS. 1 to 8 , the video encodingapparatus 100 and the video decoding apparatus 800 can perform the interprediction encoding and inter prediction decoding after enhancing theresolution of the motion vector and the reference picture byinterpolating the reference picture in the unit of sub-pixels.Specifically, they can enhance the resolution of the motion vector byinterpolating the reference picture with the same resolution in the unitof pictures or picture groups.

However, an inter prediction with an enhanced resolution of a referencepicture enables a more precise inter prediction and thus reduces thequantity of bits generated by the encoding of the residual signal.However, the enhancement of the resolution of the reference picture alsoresults in an inevitable an enhancement of the resolution of the motionvector, which increases the quantity of bits generated by encoding ofthe motion vector. As a result, even the inter prediction with anenhanced resolution of a reference picture may fail to significantlyincrease the encoding efficiency or may rather degrade the encodingefficiency depending on the images.

The following description discusses a method and an apparatus for interprediction encoding and inter prediction decoding, which can adaptivelyenhance the resolution of a reference picture in the unit of areashaving predetermined regular or irregular sizes, such as pictures,slices, and blocks of images according to the characteristics of theimages, so that an area having a relatively complex image or smallermovements is inter prediction encoded and decoded with an enhancedresolution while an area having a relatively simple image or largermovements is inter prediction encoded and decoded with a loweredresolution.

FIG. 9 is a block diagram illustrating a video encoding apparatusaccording to the first aspect of the present disclosure.

A video encoding apparatus 900 using an adaptive motion vector accordingto the first aspect of the present disclosure may include an interprediction encoder 910, a resolution change flag generator 920, aresolution determiner 930, a resolution encoder 940, and a differentialvector encoder 950. Meanwhile, it is not required but optional that allof the resolution change flag generator 920, resolution encoder 940, andthe differential vector encoder 950 be included in the video encodingapparatus 900, and they may be selectively included in the videoencoding apparatus 900.

The inter prediction encoder 910 performs an inter prediction encodingof a video in the unit of areas of the image by using a motion vectoraccording to a motion vector resolution determined for each motionvector or each area of the video. The inter prediction encoder 910 canbe implemented by the video encoding apparatus 100 described above withreference to FIG. 1 . In this event, when one or more components betweenthe resolution encoder 940 and the differential vector encoder 950 ofFIG. 9 are additionally included and the function of the additionallyincluded component or components overlaps with the function of theencoder 150 within the inter prediction encoder 910, the overlappingfunction may be omitted from the encoder 150. Further, if there is anoverlapping area between the function of the predictor 110 within theinter prediction encoder 910 and the function of the resolutiondeterminer 930, the overlapping function may be omitted from thepredictor 110.

Further, one or more components between the resolution encoder 940 andthe differential vector encoder 950 may be configured either as acomponent separate from the inter prediction encoder 910 as shown inFIG. 9 or as a component integrally formed with the encoder 150 withinthe inter prediction encoder 910. Further, the flag informationgenerated in the resolution change flag generator 920 may be transformedinto a bitstream either by the resolution change flag generator 920 orby the encoder 150 within the inter prediction encoder 910.

However, although the above description with reference to FIG. 1discusses encoding of a video in the unit of blocks by the videoencoding apparatus 100, the inter prediction encoder 910 may divide thevideo into areas with various shapes or sizes, such as blocks includingmacroblocks or subblocks, slices, or pictures, and perform the encodingin the unit of areas each having a predetermined size. Such apredetermined area may be not only a macroblock having a size of 16×16but also blocks with various shapes or sizes, such as a block having asize of 64×64 and a block having a size of 32×16.

Further, although the video encoding apparatus 100 described above withreference to FIG. 1 performs an inter prediction encoding using motionvectors having the same motion vector resolution for all the blocks ofan image, the inter prediction encoder 910 may perform an interprediction encoding by using motion vectors having motion vectorresolutions differently determined according to the video areas. Thevideo areas according to which the motion vector resolutions may bedifferently determined may be pictures (frames or fields), slices, orimage blocks each having a predetermined size.

That is, in the inter prediction encoding of an area, the interprediction encoder 910 performs a motion estimation after enhancing theresolution of the area by interpolating a reference picture which hasbeen previously encoded, decoded, and reconstructed. For theinterpolation of the reference picture, various interpolation filters,such as a Wiener filter, a bilinear filter, and a Kalman filter may beused and there may be resolutions applicable in the unit of variousinteger pixels or fraction pixels, such as 2/1 pixel, 1/1 pixel, ½pixel, ¼ pixel, and ⅛ pixel. Further, according to such variousresolutions, there may be different filter coefficients or differentnumbers of filter coefficients to be used. For example, a Wiener filtermay be used for the interpolation when the resolution corresponds to the½ pixel unit and a Kalman filter may be used for the interpolation whenthe resolution corresponds to the ¼ pixel unit.

Moreover, different numbers of filter taps may be used for theinterpolation of the respective resolutions. For example, an 8-tapWiener filter may be used for the interpolation when the resolutioncorresponds to the ½ pixel unit and a 6-tap Wiener filter may be usedfor the interpolation when the resolution corresponds to the ¼ pixelunit.

Further, the inter prediction encoder 910 may determine an optimumfilter coefficient, which has minimum errors between a picture to becurrently encoded and a reference picture, for each motion vectorresolution and then encode the filter coefficient. In this event, any ofthe Wiener filter, Kalman filter, etc. may be used with arbitrary numberof filter taps, and each resolution may prescribe distinctive numbers ofthe filters and filter taps.

In addition, the inter prediction encoder 910 may perform an interprediction by using reference pictures interpolated using differentfilters depending on the resolutions of motion vectors or areas. Forexample, as noted from Equation 2 below, in order to calculate anoptimum filter coefficient, which has a minimum Sum of SquaredDifference (SSD) between a picture to be currently encoded and areference picture, the Wiener filter may be used for calculating anoptimum filter tap for each resolution.

$\begin{matrix}{\mspace{79mu}{{\left( e^{sp} \right)^{2} = {\sum\limits_{x}{\sum\limits_{y}\left( {S_{x,y} - {\sum\limits_{i}{\sum\limits_{j}{h_{i,j}^{sp}P_{{\overset{\sim}{x} - i},{\overset{\sim}{y} - j}}}}}} \right)^{2}}}}\mspace{79mu}{S_{x,y}:{{Current}\mspace{14mu}{frame}\mspace{31mu}{P_{x,y}:{{Reference}\mspace{14mu}{{frame}\left( {\overset{\sim}{x}\mspace{14mu}{and}\mspace{14mu}\overset{\sim}{y}\mspace{14mu}{indicate}\mspace{14mu}{positions}\mspace{14mu}{at}\mspace{14mu}{which}\mspace{14mu}{the}\mspace{14mu}{motion}\mspace{14mu}{vectors}\mspace{14mu}{are}\mspace{14mu}{applied}} \right)}}}}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

In Equation 2, S indicates a pixel of the current picture, h^(sp)indicates a filter coefficient of the pixel domain, P indicates a pixelof a reference picture, e^(sp) indicates an error, and x and y indicatelocations of the current pixel.

That is, the inter prediction encoder 910 may calculate the filtercoefficient for each resolution by using a Wiener-Hopf Equation likeEquation 2, encode an optimum filter coefficient for each resolution,and include the encoded filter coefficient in a bitstream. Then, theinter prediction encoder 910 may perform an interpolation filtering forthe reference picture and then generate and encode a reference picturefor each resolution. In this event, a filter coefficient of a 6-tapWiener filter may be calculated and encoded for the ½ resolution, afilter coefficient of an 8-tap Kalman filter for the ¼ resolution, and afilter coefficient of a linear filter for the ⅛ resolution, includingthe encoded filter coefficients in the bitstream, and the referencepicture for each resolution may be then interpolated and encoded. In theencoding, the inter prediction encoder 910 may use the reference pictureinterpolated by the 6-tap Wiener filter when the resolution of thecurrent area or motion vector is the ½ resolution, and may use areference picture interpolated by the 8-tap Kalman filter when theresolution of the current area or motion vector is the ¼ resolution.

The resolution change flag generator 920 may generate a resolutionchange flag into the bitstream, which indicates whether to define amotion vector resolution and/or a resolution of a differential motionvector with respect to each area of an image or each motion vector. Thearea for the change of a motion vector resolution and/or a resolution ofa differential motion vector by the resolution change flag may be ablock, a macroblock, a group of blocks, a group of macroblocks, or anarea having a predetermined size, such as M×N. Therefore, the resolutionchange flag generator 920 may generate the resolution change flag intothe bitstream, which indicates whether to perform the inter predictionencoding by using motion vectors having a fixed motion vector resolutionfor sub-areas within a part of or all of areas of a video or whether todetermine a motion vector resolution of each area (or motion vector),perform an inter prediction encoding by using a motion vector having thedetermined motion vector resolution, and generate a differential motionvector having a fixed resolution. Such a resolution change flag may bedetermined and generated either according to configuration informationinput by a user or according to a preset determination criteria based onan analysis of the video to be encoded. The resolution change flag maybe included in a bitstream header such as a picture parameter set, asequence parameter set, or a slice header.

When the resolution change flag generated by the resolution change flaggenerator 920 indicates fixation of the motion vector resolution and/orresolution of the differential motion vectors, the inter predictionencoder 910 performs an inter prediction encoding of each of thesub-areas defined in the header by using motion vectors of the sub-areashaving the fixed motion vector resolution. For example, when aresolution change flag included in a slice header of a slice indicatesthat the motion vector resolution is fixed, the inter prediction encoder910 may determine a motion vector resolution having the lowestrate-distortion cost for an image of the slice and then perform an interprediction encoding for all areas of the slice by using motion vectorsof the areas having the determined motion vector resolution.

Further, when the resolution change flag indicates that the resolutionsof the motion vectors and/or differential motion vectors are adaptivelychanging for each area or motion vector, the inter prediction encoder910 performs an inter prediction encoding of each area by using a motionvector of each area having a motion vector resolution determined by theresolution determiner 930. For example, when a resolution change flagincluded in a slice header of a slice indicates that the resolutions ofthe motion vector and/or differential motion vector adaptively changesfor each area or motion vector, the inter prediction encoder 910 mayperform an inter prediction encoding of each area within the slice byusing a motion vector of the area having a motion vector resolutiondetermined by the resolution determiner 930. As another example, when aresolution change flag included in a slice header of a slice indicatesthat the motion vector resolution of the motion vector and/ordifferential motion vector adaptively changes for each motion vector,the inter prediction encoder 910 may perform an inter predictionencoding of each motion vector within the slice by using a motion vectorresolution determined for the motion vector by the resolution determiner930.

When a resolution change flag indicating that the motion vectorresolution of the motion vectors and/or differential motion vectorsadaptively changes foe each area or motion vector is generated by theresolution change flag generator 920, the resolution determiner 930determines an optimum motion vector resolution and/or differentialmotion vector resolution of each motion vector and/or differentialmotion vector through changing the motion vector resolution and/ordifferential motion vector resolution by using a predetermined costfunction, such as a rate-distortion cost (RD cost). In this event, theoptimum motion vector resolution and/or differential motion vectorresolution simply refers to a resolution of a motion vector and/ordifferential motion vector determined by using a predetermined costfunction and does not imply that the determined optimum motion vectorresolution and/or differential motion vector resolution always has anoptimum performance. When the predetermined cost function is arate-distortion cost, a motion vector resolution and/or differentialmotion vector resolution having the lowest rate-distortion cost may bethe optimum motion vector resolution and/or differential motion vectorresolution.

The resolution encoder 940 may encode the optimum motion vectorresolution and/or differential motion vector resolution determined foreach area or motion vector. That is, the resolution encoder 940 mayencode a motion vector resolution identification flag for indicating amotion vector resolution and/or a differential motion vector resolutionidentification flag indicating a differential motion vector resolutionof each area determined by the resolution determiner 930 and theninclude the encoded resolution identification flag in a bitstream. Theremay be various ways for implementing the motion vector resolutionidentification flag or differential motion vector resolutionidentification flag. The resolution indicated by the resolutionidentification flag may be adopted by either only one or both of amotion vector resolution and a differential motion vector resolution.

The differential vector encoder 950 may encode a differential motionvector corresponding to a difference between a predicted motion vectorand a motion vector according to a motion vector resolution determinedfor each motion vector or area. The differential motion vector may bedifferentially encoded according to the differential motion vectorresolution.

A resolution identification flag indicating a motion vector resolutionmay indicate either one of the resolutions of x component and ycomponent of a motion vector for motion estimation or both. That is,when a camera taking an image moves or when an object within a videomoves, the resolution determiner 930 may separately determine theresolutions of the x component and the y component of the motion vector.For example, the resolution determiner may determine a resolution in ⅛pixel unit for an x component of a motion vector of a certain area as itdetermines a resolution in ½ pixel unit for a y component of the motionvector. Then, the inter prediction encoder 910 may determine the motionvector of the corresponding area in different resolutions for the xcomponent and the y component and perform motion estimation and motioncompensation by using the determined motion vector, so as to perform aninter prediction encoding of the area.

FIG. 22 illustrates optimum motion vectors of a current block andsurrounding blocks in order to describe a process of determining theresolution of a motion vector by the resolution determiner 930.

When a flag which indicates that the motion vector resolution and/ordifferential motion vector resolution adaptively changes according tothe area or motion vector, is generated by the resolution change flaggenerator 920 (in the second aspect, a resolution appointment flaggenerated by a resolution appointment flag generator 3220 enablessetting of whether to change or fix the motion vector resolution and/ordifferential motion vector resolution), it is assumed that the kinds ofresolutions of the current block and surrounding blocks are ½, ¼, and ⅛and an optimum resolution has been determined as shown in FIG. 22 . Onthis assumption, block A has a resolution of ½ and a motion vector of (4/2, − 8/2), block B has a resolution of ¼ and a motion vector of (36/4, − 28/4), block C has a resolution of ⅛ and a motion vector of (136/8, − 104/8), and the current block has a resolution of ¼ and amotion vector of ( 16/4, 20/4). In this event, the predicted motionvector may follow the resolution of the current motion vector. Then, inorder to calculate the predicted motion vector, a resolution conversionprocess may be carried out to equalize the resolution of the surroundingmotion vectors to the resolution of the current motion vector.

FIG. 23 illustrates a table showing conversion formulas according to themotion vector resolutions, and FIG. 24 illustrates a table showing theresolutions of motion vectors of surrounding blocks converted based onblock X to be currently encoded.

The predicted motion vector may be obtained by using surrounding motionvectors. If the surrounding motion vectors have been stored according totheir respective resolutions and are different from the current motionvector, the conversion can be made using a multiplication and adivision. Further, in this event, the resolution conversion process maybe performed at the time of obtaining a predicted motion vector.Otherwise, if the surrounding motion vectors have been stored based onthe best resolution and the resolution of the current motion vector isnot the best resolution, the conversion can be made using a division.Further, in this event, when the resolution conversion process finds anencoded motion vector which is in less than the highest resolution, itmay carry out a resolution conversion into the heist resolution.Otherwise, if the surrounding motion vectors have been stored based on acertain reference resolution and the resolution of the current motionvector is different from the reference resolution in which thesurrounding motion vectors are stored, the conversion can be made usinga multiplication and a division. Further, in this event, when theresolution conversion process finds an encoded motion vector which isstored in a resolution different from the reference resolution, it maycarry out a resolution conversion into the reference resolution. In thecase of performing the division, rounding may be used, including around-off, a round-up, and a round-down. In the aspect shown in FIGS. 23and 24 , a round-off is used. Further, in the shown aspect, surroundingmotion vectors in store according to their respective resolutions.

A predicted motion vector may be obtained by referring to the tableshown in FIG. 23 . In FIG. 23 , the predicted motion vector can beobtained by using a median function, and a median value can be obtainedfor each component.MVPx=median( 16/4, 36/4, 32/4)= 32/4MVPy=median(− 32/4, − 28/4, − 28/4)=− 28/4

As a result, the predicted motion vector has a value of ( 32/4, − 28/7).Then, a differential motion vector is obtained by using the obtainedpredicted motion vector. The differential motion vector can be obtainedby using the difference between the motion vector and the predictedmotion vector as noted from Equation 3 below.MVD(− 16/4, 48/4)=MV( 16/4, 20/4)−MVP( 32/4, − 28/4)   Equation 3

Therefore, the differential motion vector has a value of (− 16/4, 48/4),which is equal to (−4, 12).

FIG. 25 illustrates a code number table of a differential motion vectoraccording to the motion vector resolutions.

The differential vector encoder 950 may use the code number table ofdifferential motion vectors according to the motion vector resolutionsas shown in FIG. 25 in encoding the differential motion vectors withrespect to motion vector values of respective resolutions.

Further, the predicted motion vector may be obtained as follows by usingthe example shown in FIG. 22 . In this event, instead of converting thesurrounding motion vectors according to the current resolution, it ispossible to first obtain medians of individual components of eachsurrounding motion vector.MVPx=median( 4/2, 36/4, 136/8)= 36/4MVPy=median(− 8/2, − 28/4, − 104/8)=− 104/8

As a result, the predicted motion vector has a value of ( 36/4, −104/8). The differential motion vector is obtained using the predictedmotion vector obtained as in the way as described above. Thedifferential motion vector can be obtained using the difference betweenthe motion vector and the predicted motion vectors as noted fromEquation 4 below.MVD(− 20/4, 72/4)=MV( 16/4, 20/4)−MVP( 36/4, − 104/8)   Equation 4

As a result, the differential motion vector has a value of (− 20/4,72/4), which is equal to (−5, 18).

The differential vector encoder 950 may use the code number table ofdifferential motion vectors according to the motion vector resolutionsas shown in

FIG. 25 in encoding the differential motion vectors with respect tomotion vector values for each of the resolutions.

Further, the predicted motion vectors may be obtained as follows byusing the example shown in FIG. 22 . In this event, converting thesurrounding motion vectors according to the current resolution may beperformed only after medians of individual components of eachsurrounding motion vector are obtained.MVPx=median( 4/2, 36/4, 136/8)= 36/4MVPy=median(− 8/2, − 28/4, − 104/8)=− 104/8

As a result, the predicted motion vector has a value of ( 36/4, − 52/4)with reference to FIG. 23 . The differential motion vector is obtainedusing the predicted motion vector obtained in the way as describedabove. The differential motion vector can be obtained using thedifference between the motion vector and the predicted motion vectors asnoted from Equation 5 below.MVD(− 20/4, 72/4)=MV( 16/4, 20/4)−MYP( 36/4, − 52/4)   Equation 5

As a result, the differential motion vector has a value of (− 20/4,72/4) which is equal to (−5, 18).

The differential vector encoder 950 may use the code number table ofdifferential motion vectors according to the motion vector resolutionsas shown in FIG. 25 in encoding the differential motion vectors withrespect to motion vector values for each of the resolutions.

Further, the predicted motion vectors may be obtained as follows byusing the example shown in FIG. 22 . The median can be obtained usingonly surrounding motion vector or vectors having the same resolution asthat of the current motion vector. In FIG. 22 , since only block Bcorresponds to the surrounding motion vector having the same resolutionas that of the current motion vector, the predicted motion vector has avalue of ( 36/4, − 28/4). The differential motion vector is obtainedusing the predicted motion vector obtained in the way as describedabove. The differential motion vector can be obtained using thedifference between the motion vector and the predicted motion vectors asnoted from Equation 6 below.MVD(− 20/4, 48/4)=MV( 16/4, 20/4)−MVP( 36/4, − 28/4)   Equation 6

As a result, the differential motion vector has a value of (− 20/4,48/4) which is equal to (−5, 12).

The differential vector encoder 950 may use the code number table ofdifferential motion vectors according to the motion vector resolutionsas shown in FIG. 25 in encoding the differential motion vectors withrespect to motion vector values for each of the resolutions.

Further, if the surrounding motion vectors have been stored based on aresolution of ⅛, the predicted motion vector may be obtained in the wayas described below by using the example shown in FIG. 22 . Referring toFIGS. 23 and 24 , the predicted motion vector has a value of ( 32/4, −28/4). The differential motion vector is obtained using the predictedmotion vector obtained in the way as described above. The differentialmotion vector can be obtained by using the difference between the motionvector and the predicted motion vectors as noted from Equation 3. As aresult, the differential motion vector has a value of (− 16/4, 48/4)which is equal to (−4, 12).

Meanwhile, the resolution encoder 940 may encode the kinds ofresolutions and the resolution change flag (the resolution appointmentflag in the second aspect) into the header. In this event, theresolution encoder 940 may encode the resolution identification flag,which has been determined as the optimum flag, to ¼, and thedifferential vector encoder 950 may encode the differential motionvector obtained by using a predicted motion vector calculated by usingthe surrounding motion vectors converted according to the resolutiondetermined by the resolution determiner 930.

FIG. 26 illustrates optimum motion vectors of a current block andsurrounding blocks in order to describe a process of determining aresolution of a differential motion vector by the resolution determiner930.

As noted from FIG. 26 , if the motion vector resolution of the currentblock and surrounding blocks is ⅛, the predicted motion vector may becalculated by Equation 7 below.PMVx=median(⅞, ⅛, 2/8)= 2/8PMVy=

(− 6/8, ⅛, − 2/8)=− 2/8  Equation 7

As a result, PMV=( 2/8, − 2/8)=(¼, −¼). The differential motion vectorcan be obtained by Equation 8 below.MVD (−⅛, − 2/8)=MV(⅛, − 4/8)−PMV(¼, −¼)   Equation 8

Therefore, the differential motion vector identification flag MVDx maybe encoded to ⅛ and the differential motion vector identification flagMVDy may be encoded to ¼.

FIG. 27 illustrates a code number table of differential motion vectorsaccording to the differential motion vector resolutions.

As noted from FIG. 27 , the code number of the differential motionvector is (1, 1) according to the code number table of the differentialmotion vector. Therefore, the resolution encoder 940 may encode x and ycomponents of the differential motion vector resolution identificationflag to (⅛, ¼), encode the code number of the differential motion vectorto (1, 1), and separately encode signs of the x and y components of thedifferential motion vector.

Meanwhile, when the differential vector encoder 950 encodes thedifferential motion vector, it determines a reference resolution orconverts a motion vector having a resolution, other than a referenceresolution to one with the reference resolution, and calculates adifferential motion vector by using a reference predicted motion vectorobtained from a reference motion vector of surrounding blocks. If amotion vector has a resolution other than the reference resolution,there is a method of additionally encoding a reference resolution flag.The reference resolution flag may include data indicating whether themotion vector has the same resolution as the reference resolution anddata indicating a location of the actual motion vector.

The reference resolution may be defined in a header, such as a pictureparameter set, a sequence parameter set, or a slice header.

FIG. 28 illustrates a motion vector of the current block X and areference motion vector of surrounding blocks.

When the resolution change flag (the resolution appointment flag in thesecond aspect) indicates multiple resolutions, the kinds of theresolutions include ½, ¼, and ⅛, the reference resolution is ¼, and theoptimum resolution has been determined as shown in FIG. 28 , the currentmotion vector ( 4/8, ⅝) is converted by using the reference resolution,¼, to a reference motion vector by Equation 9 below.Ref_MVx= 2/4Ref_MVy=¾  Equation 9

If the resolution of the current motion vector is different from thereference resolution, it may be converted by using a multiplication anda division. In the case of using the division, rounding may be usedincluding a round-off, a round-up, and a round-down. The current aspectuses a round-off. Therefore, the reference resolution has a value of (2/4, ¾), and the location of the actual motion vector having aresolution other than the reference resolution can be expressed usingthe reference resolution flag. In this event, the difference between themotion vector of the current block and the reference motion vector is(0, ⅛), and the value of the reference resolution flag may have, forexample, location information, such as (0, 1). In the example of thelocation information, (0, 1), “0” indicates that the reference motionvector is equal to the motion vector and “1” indicates a motion vectorthat is smaller by −⅛ than the reference motion vector.

In the meantime, the differential vector of the reference motion vectoris calculated using a predicted reference motion vector, whichcorresponds to a median value of the reference motion vector of thesurrounding blocks.Ref_PMVx=median( 9/4, 1, 2/4)=1Ref_PMVy=median(− 7/4, −1, −1)=−1   Equation 10

Therefore, the predicted reference motion vector Ref_PMV has a value of(1, −1). Then, by applying (Ref_MV( 2/4, ¾)−Ref_PMV(1, −1)), thedifferential reference motion vector Ref_MVD has a value of (− 2/4,7/4). Therefore, the encoder encodes the Ref_MVD (− 2/4, 7/4) andencodes the reference resolution flag (0, 1).

FIG. 29 illustrates a code number table of a differential referencemotion vector according to the differential reference motion vectorresolution.

Referring to FIG. 29 , the code number is 2 when the referenceresolution is ¼ and the value of the differential reference motionvector is 2/4, and the code number is 3 when the reference resolution is¼ and the value of the differential reference motion vector is ¾, andthe code number of each component of the differential reference motionvector is included in the reference resolution flag.

The resolution encoder 940 can encode in various ways the motion vectorresolution and/or differential motion vector resolution determinedaccording to each motion vector or area. The following description withreference to FIGS. 10 to 14 discusses various examples of the encodingof the motion vector resolution or differential motion vectorresolution. Although the following description deals with only theexamples of the encoding of the motion vector resolution, thedifferential motion vector resolution can also be encoded in the sameway as that for the motion vector resolution, which is omitted in thedescription.

The resolution encoder 940 may integrate the motion vector resolutionsand/or differential motion vector resolutions of adjacent areas havingthe same motion vector resolution with each other, and then generate aresolution identification flag for each integrated area. For example,the resolution encoder 940 may hierarchically generate the resolutionidentification flags with a Quadtree structure. In this event, theresolution encoder 940 may encode an identifier, which represents themaximum number of the Quadtree layers and the size of the area indicatedby the lowest node of the Quadtree layers, and then include the encodedidentifier in a header of a corresponding area of a bitstream.

FIGS. 10A to 10C illustrate an example of motion vector resolutionshierarchically expressed by a Quadtree structure according to an aspectof the present disclosure.

FIG. 10A illustrates areas having various motion vector resolutionswithin one picture. In FIG. 10A, each area may be a macroblock having asize of 16×16 and the number in each area indicates a motion vectorresolution of the area. FIG. 10B illustrates grouping of the areas shownin FIG. 10A into grouped areas, each of which includes areas having thesame motion vector resolution. FIG. 100 hierarchically illustrates themotion vector resolutions of the grouped areas shown in FIG. 10B in aQuadtree structure. As noted from FIG. 100 , the area indicated by thelowest node corresponds to a macroblock having a size of 16×16 and themaximum number of the layers of the Quadtree structure is 4. Therefore,this information is encoded and is included in a header for thecorresponding area.

FIG. 11 illustrates a hierarchically expressed result of encoded motionvector resolutions in a Quadtree structure according to an aspect of thepresent disclosure.

The final bits as shown in FIG. 11 can be obtained by encoding themotion vector resolutions in the Quadtree structure shown in FIG. 100 .One encoded bit may indicate whether a node has been divided. Forexample, a bit value of “1” may indicate that a corresponding node hasbeen divided into lower nodes and a bit value of “0” may indicate that acorresponding node has not been divided into the lower layers.

In FIG. 100 , since the node of level 0 has been divided into lowerlayers, it is encoded to a bit value of “1”. Since the first node ofdivided level 1 has a resolution of ½ and has not been divided any more,it is encoded to a bit value of “0” while the motion vector resolutionof ½ is encoded. Since the second node of level 1 has been divided intolower layers, it is encoded to a bit value of “1”. Since the third nodeof level 1 has not been divided into lower layers, it is encoded to abit value of “0” while the motion vector resolution ¼ is encoded. Sincethe final fourth node of level 1 has been divided into lower layers, itis encoded to a bit value of “1”. Nodes of level 2 are encoded in thesame way. In level 3, only the motion vector resolutions are encoded,because the maximum number of layers has been determined as 3 in theheader, which tells that there are no more layers lower than level 3.The final bits generated by hierarchically encoding the various motionvector resolutions of the areas shown in FIG. 10A in a Quadtreestructure may have the structure as shown in FIG. 11 .

The motion vector resolutions of ½, ¼, and ⅛ identified in the finalbits imply the encoding result of using their representative bits,although the bit values are not represented for the convenience ofdescription. The motion vector resolutions may be expressed by bitvalues in various ways according to the implementation methods. Forexample, if there are two type of available motion vector resolutions,they can be indicated by a 1-bit flag. Further, if there are four orless types of available motion vector resolutions, they can be indicatedby a 2-bit flag.

If the maximum number of layers and the size of the area indicated bythe lowest node are defined in a slice header, the resolutionidentification flag generated as described above may be included in thefield of the slice data. A video decoding apparatus, which will bedescribed later, can extract and decode a resolution identification flagfrom a bitstream, so as to reconstruct the motion vector resolution ofeach area.

Further, the aspect shown in FIGS. 10A to 10C discusses only twoalternative cases in which a node is either divided into lower layers(i.e. four areas) or undivided, although there may be various divisionsas shown in FIG. 20 , including the nondivision of the node, itsdivisions into two transversely lengthy areas, two longitudinallylengthy areas, or four areas.

Further, the resolution encoder 940 may generate a resolutionidentification flag by encoding the motion vector resolution of eacharea or motion vector by using a predicted motion vector resolutionpredicted by motion vector resolutions of surrounding areas of thatarea. For example, based on an assumption that an area corresponds to ablock having a size of 64×64, the motion vector resolution of the areamay be predicted by using motion vector resolutions of areas at the leftside and upper side of the area. When the predicted motion vectorresolution of an area is identical to the motion vector resolution ofthe area, the resolution encoder 940 may encode a resolutionidentification flag of the area to a bit value of “1”. Otherwise, whenthe predicted motion vector resolution of an area is not identical tothe motion vector resolution of the area, the resolution encoder 940 mayencode a resolution identification flag of the area to a bit value of“0” and a bit value indicating a motion vector resolution of the area.For example, if each of the resolutions of the upper area and the leftarea of an area is ½ and the resolution of the area is also ½, theresolution encoder 940 may encode the resolution identification flag ofthe area to a bit value of “1” and does not encode the motion vectorresolution of the area. If each of the resolutions of the upper area andthe left area of an area is ½ and the resolution of the area is ¼, theresolution encoder 940 may encode the resolution identification flag ofthe area to a bit value of “0” and may additionally encode the motionvector resolution of the area.

Further, the resolution encoder 940 may generate a resolutionidentification flag by encoding the motion vector resolution of eacharea of motion vector by using the run and length of the motion vectorresolution of each area or motion vector.

FIG. 12 illustrates motion vector resolutions of areas determinedaccording to an aspect of the present disclosure.

In FIG. 12 , areas within one picture correspond to macroblocks eachhaving a size of 16×16 and a motion vector resolution of each area isexpressed in each area. Hereinafter, an example of encoding the motionvector resolutions of the areas shown in FIG. 12 by using the runs andlengths thereof will be described. When the motion vector resolutions ofthe areas shown in FIG. 12 are ordered in a raster scan direction, themotion vector resolution of ½ occurs four times in a row, the motionvector resolution of ¼ once, the motion vector resolution of ⅛ twice ina row, and the motion vector resolution of ½ is four times in a row (themotion vector resolutions thereafter are omitted). As a result, usingthe runs and lengths, those motion vector resolutions can be expressedas (½, 4), (¼, 1), (⅛, 2), (½, 4), . . . . Therefore, the resolutionencoder 940 can generate a resolution identification flag by encodingthe motion vector resolution of each area expressed using the run andlength and expressing the resolution by a bit value.

Further, the resolution encoder 940 may generate a resolutionidentification flag by hierarchically encoding the motion vectorresolutions of each area or motion vector by using a tag tree. In thisevent, the resolution encoder 940 may include an identifier whichindicates the maximum number of the tag tree layers and the size of thearea indicated by the lowest node, in a header.

FIG. 13 illustrates an example of motion vector resolutionhierarchically expressed in a tag tree structure according to an aspectof the present disclosure.

In particular, FIG. 13 shows the hierarchical tag tree structure of themotion vector resolution respectively determined for the individualareas within a section of an image. It is assumed that each of the areascorresponds to a macroblock having a size of 16×16.

In FIG. 13 , since the minimum value is ½ among the motion vectorresolutions of the first four areas of level 3, the motion vectorresolution of the first area is ½. The areas are hierarchically groupedin this way as many times as the number of layers, and coded bits arethen generated from each upper layer to its lower layer to complete theencoding stage thereof.

FIG. 14 illustrates a result of the encoding of the motion vectorresolutions hierarchically expressed in a tag tree structure accordingto an aspect of the present disclosure.

In a method of generating a coded bit of each area, subtracted valuesbetween the motion vector resolution number designations in currentlayers and their higher layers from the root to end nodes of the treeare expressed by a series of “0” finished with the last bit value of“1”. In this event, in the case of the highest layer, based on anassumption that a motion vector resolution of its higher layer isdesignated “0”, a motion vector resolution of ½ is “1”, a motion vectorresolution of ¼ is “2”, and a motion vector resolution of ⅛ is “3”, aresolution identification flag may be generated as shown in FIG. 14 byhierarchically encoding the motion vector resolutions of the areas asshown in FIG. 13 with the tag tree structure. In this event, the numberassigned to each motion vector resolution may be changed.

In FIG. 14 , pair of numbers (0,0), (0,1), etc. expressed in therespective areas correspond to reference numbers identifying the areas,and numerals “0111”, “01”, etc. correspond to bit values of resolutionidentification flags obtained by encoding the motion vector resolutionsof the areas.

In the case of the resolution identification flag in the area identifiedby (0,0), Level 0 has its higher layer motion vector resolution numbered“0” as Level 1 has the motion vector resolution of ½ numbered “1”leading to subtracted value between the Level 1 number and the Level 0number into “1” which is converted to a coded bit of “01”. Again, Level1 has a difference from its higher layer (Level 0) in their motionvector resolution numbers by subtracted value “0” which turns to a codedbit of “1”. Yet again, Level 2 has a difference from its upper layer(Level 1) in their motion vector resolution numbers by subtracted value“0” which turns to a coded bit of “1”. Furthermore, in Level 3, sincethe difference between the numbers of the motion vector resolutions ofLevel 3 and the higher layer (Level 2) is “0”, an encoded bit of “1” isobtained. As a result, “0111” is finally obtained as encoded bits of themotion vector resolution of the area identified by (0,0).

In the case of the resolution identification flag of the area identifiedby (0,1), Level 0, Level 1, and Level 2 are already reflected in theresolution identification flag identified by (0,0). Therefore, only inLevel 3, “1”, which is the difference between the numbers of the motionvector resolutions of Level 3 and the higher layer (Level 2), isencoded, so as to obtain an encoded bit of “01”. As a result, only “01”is finally obtained as a resolution identification flag of the areaidentified by (0,1).

In the case of the resolution identification flag of the area identifiedby (0,4), Level 0 is already reflected in the resolution identificationflag identified by (0,0). Therefore, only Level 1, Level 2, and Level 3are subjected to an encoding in the way described above, so that “0111”is finally obtained as the encoded bits.

Further, the resolution encoder 940 may generate a resolutionidentification flag by changing and encoding the number of bitsallocated to the motion vector resolution according to the frequency ofthe motion vector resolution determined for each motion vector or area.To this end, the resolution encoder 940 may change and encode the numberof bits allocated to the motion vector resolution of a correspondingarea according to the occurrence frequency of the motion vectorresolution up to the just previous area in the unit of area, or maychange and encode the number of bits allocated to the motion vectorresolution of a corresponding section, which includes a plurality ofareas, according to the occurrence frequency of the motion vectorresolution up to the just previous section or the occurrence frequencyof the motion vector resolution of the just previous section in the unitof sections. To this end, the resolution encoder 940 may encode themotion vector resolution of each area by calculating the frequency ofthe motion vector resolution in the unit of areas or sections,allocating numbers to the motion vector resolutions in a sequencecausing the smaller number to be allocated to a motion vector resolutionhaving the larger frequency, and allocating the smaller number of bitsto the motion vector resolutions allocated the smaller numbers.

For example, in the case where the resolution encoder 940 changes thebit numbers according to the occurrence frequency of the motion vectorresolution up to the previous area in the unit of areas, if the motionvector resolution of ½ has occurred 10 times, the motion vectorresolution of ¼ has occurred 15 times, and the motion vector resolutionof ⅛ has occurred 8 times in all areas up to the previous area, theresolution encoder 940 allocates the smallest number (e.g. No. 1) to themotion vector resolution of ¼, the next smallest number (e.g. No. 2) tothe motion vector resolution of ½, and the largest number (e.g. No. 3)to the motion vector resolution of ⅛, and allocates a smaller number ofbits to the motion vector resolutions in a sequence from the smallernumber to the larger number. Then, if the motion vector resolution ofthe area, for which the motion vector resolution is to be encoded,corresponds to the ¼ pixel unit, the resolution encoder 940 may allocatethe smallest bits to the motion vector resolution, so as to encode themotion vector resolution of ¼ for the area.

Further, in the case where the resolution encoder 940 changes andencodes the bit numbers according to the frequency of occurrences of themotion vector resolution up to the previous area group in the unit ofarea groups, the resolution encoder 940 may encode the motion vectorresolution of each area of the area group, for which the motion vectorresolution is to be encoded, by updating the occurrence frequency of themotion vector resolution of each area up to the previous area group,allocating numbers to the motion vector resolutions in a sequencecausing the smaller number to be allocated to a motion vector resolutionhaving the larger frequency, and allocating the smaller number of bitsto the motion vector resolutions allocated the smaller numbers. The areagroup may be a Quadtree, a Quadtree bundle, a tag tree, a tag treebundle, a macroblock, a macroblock bundle, or an area in a predeterminedsize. For example, when the area group is appointed as including twomacroblocks, it is possible to update the frequency of occurrence of themotion vector resolution for every two macroblocks and allocate a bitnumber of the motion vector resolution to the updated frequency.Otherwise, when the area group is appointed as including four Quadtrees,it is possible to update the frequency probability of the motion vectorresolution for every four Quadtrees and allocate a bit number of themotion vector resolution to the updated frequency.

Further, the resolution encoder 940 may use different methods forencoding a resolution identification flag according to the distributionof the motion vector resolutions of surrounding areas of each area withrespect to the motion vector resolution determined according to eacharea or motion vector. That is, the smallest bit number is allocated toa resolution having the highest probability that the resolution may bethe resolution of a corresponding area according to the distribution ofthe motion vector resolutions of surrounding areas or area groups. Forexample, if a left side area of an area has a motion vector resolutionof ½ and an upper side area of the area has a motion vector resolutionof ½, it is most probable that the area has a motion vector resolutionof ½, and the smallest bit number is thus allocated to the motion vectorresolution of ½, which is then encoded. As another example, if a leftside area of an area has a motion vector resolution of ¼, a left upperside area of the area has a motion vector resolution of ½, an upper sidearea of the area has a motion vector resolution of ½, and a right upperside area of the area has a motion vector resolution of ½, the bitnumbers are allocated to the motion vector resolutions in a sequencecausing the smaller bit number to be allocated to a motion vectorresolution having the higher probability, such as in a sequence of ½, ¼,⅛, . . . , and the motion vector resolutions are then encoded.

Further, in performing the entropy encoding by an arithmetic encoding,the resolution encoder 940 uses different methods of generating a bitstring of a resolution identification flag according to the distributionof the motion vector resolutions of the surrounding areas of each areafor the motion vector resolution determined according to each motionvector or area and applies different context models according to thedistribution of the motion vector resolutions of the surrounding areasand the probabilities of the motion vector resolution having occurred upto the present for the arithmetic encoding and probability update.

Referring to FIG. 21 as an example, based on an assumption that anentropy encoding is performed using only three motion vector resolutionsincluding ½, ¼, and ⅛ by the CABAC, if a left side area of a pertinentarea has a motion vector resolution of ½ and an upper side area of thearea has a motion vector resolution of ½, the shortest bit string isallocated to the motion vector resolution of ½ and the other bit stringsare allocated to the motion vector resolutions in a sequence causing thesmaller bit number to be allocated to a motion vector resolution havingthe higher probability. Specifically, if the motion vector resolution of⅛ has the higher occurrence probability than that of the motion vectorresolution of ¼, the bitstream of “00” is allocated to the motion vectorresolution of ⅛ and the bitstream of “01” is allocated to the motionvector resolution of ½ for the arithmetic encoding.

Further, in encoding the first bit string, four different context modelsmay be used, which include: a first context model in which theresolution of the left side area is equal to the resolution of the upperside area, which is equal to the resolution of the highest probabilityup to the present; a second context model in which the resolution of theleft side area is equal to the resolution of the upper side area, whichis different from the resolution of the highest probability up to thepresent; a third context model in which the resolutions of the left sidearea and the upper side area are different from each other and at leastone of the resolutions of the left side area and the upper side area isequal to the resolution of the highest probability up to the present;and a fourth context model in which the resolutions of the left sidearea and the upper side area are different from each other and neitherof them is equal to the resolution of the highest probability up to thepresent. In encoding the second bit string, two different context modelsmay be used, which include: a first context model in which theresolutions of the left side area and the upper side area are differentfrom each other and at least one of the resolutions of the left sidearea and the upper side area is equal to the resolution of the highestprobability up to the present; and a second context model in which theresolutions of the left side area and the upper side area are differentfrom each other and neither of them is equal to the resolution of thehighest probability up to the present.

As another example, based on an assumption that an entropy encoding isperformed using only three motion vector resolutions including ½, ¼, and⅛ by the CABAC and the highest motion vector resolution up to thepresent is ¼, “1”, which is the shortest bitstream, is allocated to themotion vector resolution of ¼ and “00” and “01” are then allocated tothe other motion vector resolutions of ½ and ⅛, respectively. Further,in encoding the first bit string, three different context models may beused, which include: a first context model in which each of theresolutions of the left side area and the upper side area of acorresponding area is equal to the resolution of the highest probabilityup to the present; a second context model in which only one of theresolutions of the left side area and the upper side area of acorresponding area is equal to the resolution of the highest probabilityup to the present; and a third context model in which neither of theresolutions of the left side area and the upper side area of acorresponding area is equal to the resolution of the highest probabilityup to the present. In encoding the second bit string, six differentcontext models may be used, which include: a first context model inwhich each of the resolution of the left side area and the resolution ofthe upper side area of a corresponding area corresponds to a motionvector resolution of ⅛; a second context model in which each of theresolutions of the left side area and the upper side area of acorresponding area corresponds to a motion vector resolution of ½; athird context model in which each of the resolutions of the left sidearea and the upper side area of a corresponding area corresponds to amotion vector resolution of ¼; a fourth context model in which one ofthe resolutions of the left side area and the upper side area of acorresponding area corresponds to a motion vector resolution of ⅛ andthe other resolution corresponds to a motion vector resolution of ¼; afifth context model in which one of the resolutions of the left sidearea and the upper side area of a corresponding area corresponds to amotion vector resolution of ½ and the other resolution corresponds to amotion vector resolution of ¼; and a sixth context model in which one ofthe resolutions of the left side area and the upper side area of acorresponding area corresponds to a motion vector resolution of ⅛ andthe other resolution corresponds to a motion vector resolution of ½. Theresolution of the highest probability up to now may be of theprobability of resolution encoded up to the previous area, a probabilityof a certain area, or a predetermined fixed resolution.

Further, the resolution encoder 940 may determine whether a videodecoding apparatus can estimate a motion vector resolution of eachmotion vector or area according to a prearranged estimation scheme.Then, for an area having an estimable motion vector resolution, theresolution encoder 940 may encode a positive identifier, which indicatesthat it can be estimated, so as to generate a resolution identificationflag. In contrast, for an area having an inestimable motion vectorresolution, the resolution encoder 940 may encode a negative identifier,which indicates that it cannot be estimated, and a motion vectorresolution of a corresponding area, so as to generate a resolutionidentification flag.

That is, in order to encode a motion vector resolution of each motionvector or area, the resolution encoder 940 calculates a motion vectorand a predicted motion vector of the area with multiple motion vectorresolutions applied, encodes a differential motion vector between them,decodes the differential motion vector, and decodes the motion vectorfor each resolution by using the reconstruction of the decodeddifferential motion vector based on assumption that each resolution isthe optimum resolution. Then, the resolution encoder 940 determines amotion vector resolution, which has the lowest cost according to apredetermined cost function when motions of surrounding pixels of acorresponding area by using the motion vector reconstructed based on anassumption that each resolution is the optimum resolution. When themotion vector resolution determined in the way described above is equalto a motion vector resolution of a corresponding area originally desiredto be encoded (i.e. a motion vector resolution determined as an optimummotion vector resolution of the corresponding area, on condition thatthe optimum motion vector resolution does not imply that it alwaysexhibits the optimum performance and simply refers to a motion vectorresolution determined as optimum under the conditions for determiningthe motion vector resolution), the resolution encoder 940 may generatean identifier (e.g. “1”), indicating that the video decoding apparatuscan estimate the motion vector resolution of the corresponding area, asa resolution identification flag of the corresponding area. In thisevent, the motion vector resolution of the corresponding area is notencoded. When the determined motion vector resolution is not equal tothe motion vector resolution of the corresponding area intended to beencoded, the resolution encoder 940 may encode an identifier (e.g. “0”),indicating that the video decoding apparatus cannot estimate the motionvector resolution of the corresponding area, and the original motionvector resolution of the corresponding area, so as to generate aresolution identification flag of the corresponding area. In this event,various distortion functions, such as Mean Square Error (MSE) or Sum ofAbsolute Transformed Differences (SATD), may be used as thepredetermined cost function.

Further, when each component of the differential motion vector is “0”,the resolution encoder 940 may dispense with encoding the resolution ofthe motion vector or area. When each component of the differentialmotion vector is “0”, a predicted motion vector is encoded to a motionvector, which makes it unnecessary to encode the motion vectorresolution.

FIG. 15 illustrates an example of a process for determining a motionvector resolution by using surrounding pixels of an area according to anaspect of the present disclosure.

Referring to FIG. 15 , if the optimum motion vector resolutiondetermined as a result of the motion estimation for an area, the motionvector resolution of which is to be encoded by the resolution encoder940, is a motion vector resolution of ½, a motion vector is (4, 10), anda predicted motion vector is (2, 7), the differential motion vector is(2, 3). In this event, based on an assumption that a video decodingapparatus can decode and reconstruct only a differential vector, theresolution encoder 940 may change the motion vector resolution intovarious motion vector resolutions, predict a predicted motion vectoraccording to each motion vector resolution, reconstruct a motion vectoraccording to each motion vector resolution, and determine a motionvector resolution having a least distortion between surrounding pixelsof a current area and surrounding pixels of an area indicated by amotion vector according to each reconstructed motion vector resolution.

If the motion vector resolution corresponds to the ¼ pixel unit and thepredicted motion vector is (3, 14), the differential motion vectorreconstructed by the video decoding apparatus is (2, 3) and the motionvector of the corresponding reconstructed area is thus (5, 17). Further,if the motion vector resolution corresponds to a ½ pixel unit and thepredicted motion vector is (2, 7), the differential motion vectorreconstructed by the video decoding apparatus is (2, 3) and the motionvector of the corresponding reconstructed area is thus (4, 10). In thesame way as described above, a motion vector of a corresponding areareconstructed by the video decoding apparatus is also calculated in thecase where the motion vector resolution corresponds to the ⅛ pixel unit.

When the motion vector resolution having a least distortion betweensurrounding pixels of a corresponding area and surrounding pixels of anarea having been motion-compensated in a reference picture by using amotion vector of a corresponding area reconstructed according to eachmotion vector resolution is equal to an optimum motion vector resolutiondetermined in advance, the resolution encoder 940 encodes only anidentifier, indicating that the video decoding apparatus can estimatethe motion vector resolution, so as to generate a resolutionidentification flag of the corresponding area, and does not encode themotion vector resolution of the corresponding area.

When the size of a predicted motion vector or differential motion vectorof a motion vector according to a motion vector resolution determinedfor each area or motion vector is larger than a threshold, theresolution determiner 930 may determine a predetermined value as themotion vector resolution of each area or motion vector. For example,when the size of a differential motion vector or the size of a predictedmotion vector of an area or a motion vector is larger than a threshold,the resolution determiner 930 may determine a predetermined value as amotion vector resolution of the area or the motion vector withoutencoding the motion vector resolution of the area. Further, when thesize of a motion vector of a surrounding area of an area or a motionvector is larger or the size of a motion vector of an area is largerthan a threshold, the resolution determiner 930 may determine apredetermined value as a motion vector resolution of the area withoutencoding the motion vector resolution of the area. In this event, themotion vector resolution of the area or motion vector can be changed toa predetermined resolution even without a flag. The threshold may be apre-appointed value or any inputted values, or may be calculated from amotion vector of a surrounding block.

When the resolution of the current block is identifiable with areference picture index, the resolution determiner 930 may encodeinformation on the resolution by encoding the reference picture indexwithout generating a resolution identification flag.

For example, based on the distance between the current picture and thereference picture as shown in FIG. 30 , the resolution determiner 930may index and encode the reference picture. For example, based on anassumption that four reference pictures are used, candidates ofreference pictures, which can be indexed when the current picture is No.5, can be indexed as shown in FIG. 31 .

FIG. 31 is a table illustrating an example of reference picture indexesaccording to reference picture numbers and resolutions.

With resolutions ¼ and ⅛ being used, in the event illustrated in FIG. 13where the optimal reference picture is numbered 3 and has the resolutionof ⅛, the reference picture index may be encoded into 3, and then thedecoding apparatus will know that the reference picture number of 3after extracting the same from the bitstream and that the resolution is⅛ by using the same table as is used by the decoder.

The differential vector encoder 950 may differently encode differentialvectors depending on the motion vector resolutions. That is, as themotion vector resolution increases, the size of the motion vector alsoincreases and the required bit quantity thus increases. Therefore, byencoding differential vectors in different ways according to the motionvector resolutions, the differential vector encoder 950 can reduce thebit quantity.

For example, when the differential vector encoder 950 encodes thedifferential vector by using the UVLC, the differential vector encoder950 may use the K-th order Exp-Golomb code in the encoding. In thisevent, the differential vector encoder 950 may change the degree oforder (K) of the Exp-Golomb code according to the motion vectorresolution determined for each area. For example, in the case ofencoding the differential vector by using the UVLC, the degree of order(K) of the Exp-Golomb code can be set to “0” when the motion vectorresolution corresponds to the ¼ pixel unit and the degree of order (K)of the Exp-Golomb code can be set to “1” when the motion vectorresolution corresponds to the ⅛ pixel unit.

Further, when the differential vector encoder 950 encodes thedifferential vector by using the CABAC, the differential vector encoder950 may use the Concatenated Truncated Unary/K-th Order Exp-Golomb Codein the encoding. In the encoding, the differential vector encoder 950may change the degree of order (K) and the maximum value (T) of theConcatenated Truncated Unary/K-th Order Exp-Golomb Code according to themotion vector resolution determined for each area. For example, in thecase of encoding the differential vector by using the CABAC, the degreeof order (K) of the code may be set to “3” and the maximum value (T) ofthe code may be set to “6” when the motion vector resolution correspondsto the ¼ pixel unit, and the degree of order (K) of the code may be setto “5” and the maximum value (T) of the code may be set to “12” when themotion vector resolution corresponds to the ⅛ pixel unit.

In addition, when the differential vector encoder 950 encodes thedifferential vector by using the CABAC, the differential vector encoder950 may differently calculate the accumulation probability according tothe motion vector resolution determined for each area. For example,whenever encoding the differential vectors of the areas, thedifferential vector encoder 950 may update each context model accordingto the motion vector resolution determined for each area, and may usethe updated context model according to each motion vector resolutionwhen encoding a differential vector of another area. That is, when amotion vector resolution of an area corresponds to the ½ pixel unit, thedifferential vector encoder 950 may encode the differential vector byusing the context model of the ½ pixel unit and update the context modelof the ½ pixel unit. Further, when a motion vector resolution of an areacorresponds to the ⅛ pixel unit, the differential vector encoder 950 mayencode the differential vector by using the context model of the ⅛ pixelunit and update the context model of the ⅛ pixel unit.

Further, in order to calculate the differential vector of each area, thedifferential vector encoder 950 may predict a predicted motion vectorfor each area or motion vector by using motion vectors of surroundingareas of each area or motion vector. In this event, when the motionvector resolution of each area is not equal to the motion vectorresolution of surrounding areas, the differential vector encoder 950 mayconvert the motion vector resolution of the surrounding areas to themotion vector resolution of said each area for the prediction. For theconverting of the motion vector resolution, it is possible to use around-off, a round-up, and a round-down. In this event, it is requiredto understand that the surrounding areas include adjacent areas.

FIG. 16 is a view for illustrating the process of predicting a predictedmotion vector according to an aspect of the present disclosure.

Referring to the example shown in FIG. 16 , if motion vectors ofsurrounding areas of an area of a predicted motion vector to bepredicted are (4, 5), (10, 7), and (5, 10) and a round-off is used forthe converting, the predicted motion vector may be (5, 5) when theresolution of the motion vector of the area to be predicted is ¼, andthe predicted motion vector may be (10, 10) when the resolution of themotion vector of the area to be predicted is ⅛.

Further, when the block mode of one or more areas among the areas is askip mode, the differential vector encoder 950 may convert the motionvector resolution of the area of the motion vector to be predicted tothe highest resolution among the motion vector resolutions ofsurrounding areas of the area and then perform the prediction. Referringto the example shown in FIG. 16 , when the area to be predicted is inthe skip mode, since the highest resolution among the motion vectorresolutions of the surrounding areas is ⅛, a predicted motion vector of(10, 10) is obtained based on an assumption that the resolution of thearea to be predicted is ⅛.

Moreover, in predicting a predicted motion vector of an area to bepredicted by using motion vectors of surrounding areas of the area, thedifferential vector encoder 950 may convert the motion vectors of thesurrounding areas to a predetermined resolution. In this event, when apredetermined motion vector resolution and the motion vector resolutionof the area to be predicted are not equal to each other, thedifferential vector encoder 950 may convert the predetermined motionvector resolution to the motion vector resolution of the area of thepredicted motion vector to be predicted, so as to obtain a finalpredicted motion vector. Referring to the example shown in FIG. 16 , thepredicted motion vector is converted to (3, 3) when the predeterminedmotion vector resolution corresponds to the ½ pixel unit. Further, whenthe motion vector resolution of the area to be predicted corresponds tothe ⅛ pixel unit, which is not equal to the predetermined motion vectorresolution, the predicted motion vector of (3, 3) is converted to the ⅛pixel unit, so as to obtain a final predicted motion vector of (12, 12).In the same way, when the motion vector resolution of the area to bepredicted corresponds to the ¼ pixel unit, it is possible to obtain afinal predicted motion vector of (12, 12).

FIG. 17 is a flowchart for describing a method for encoding a video byusing an adaptive motion vector resolution according to a first aspectof the present disclosure.

In a method for encoding a video by using an adaptive motion vectorresolution according to a first aspect of the present disclosure, amotion vector resolution is first determined for each area or motionvector, and an inter prediction encoding of a video is performed in theunit or areas by using a motion vector according to the motion vectorresolution determined for each area or motion vector. To this end, avideo encoding apparatus 900 using an adaptive motion vector resolutionaccording to a first aspect of the present disclosure determines whetherthe motion vector resolution changes according to each area or motionvector of a video (step S1710). When the motion vector resolutionchanges according to each area or motion vector, the video encodingapparatus 900 determines the motion vector resolution of each area ormotion vector (step S1720). Then, the video encoding apparatus 900performs an inter prediction encoding of the video in the unit of areasby using a motion vector according to the motion vector resolutiondetermined for each area or motion vector (step S1730). In contrast,when the motion vector resolution does not change but is fixedregardless of the area or motion vector, the video encoding apparatus900 performs an inter prediction encoding of the video in the unit ofareas by using a motion vector according to the fixed motion vectorresolution for lower areas within some areas or all areas of the video(step S1740).

In this event, the motion vector resolution determined for each area mayhave different values for an x component and a y component of the area.

Further, the video encoding apparatus 900 may generate a resolutionidentification flag, which indicates whether to determine the motionvector resolution, according to each area or motion vector. For example,when it is determined in step S1710 that the motion vector resolutionchanges according to each area or motion vector, the video encodingapparatus 900 may generate a resolution identification flag (e.g. “1”)indicating that the motion vector resolution changes according to eacharea or motion vector. Further, when it is determined in step S1710 thatthe motion vector resolution does not change but is fixed regardless ofthe area or motion vector, the video encoding apparatus 900 may generatea resolution identification flag (e.g. “0”) indicating that the motionvector resolution does not change but is fixed regardless of the area ormotion vector. In contrast, the video encoding apparatus 900 maygenerate a resolution identification flag according to the setinformation input from a user or an exterior, and may determine whetherthe motion vector resolution is determined for each area as in stepS1710 based on the bit value of the generated resolution identificationflag.

Further, the video encoding apparatus 900 may encode a motion vectorresolution determined for each area or motion vector. For example, thevideo encoding apparatus 900 may hierarchically encode the motion vectorresolutions determined for respective areas or motion vectors in aQuadtree structure by grouping areas having the same motion vectorresolution together, may encode the motion vector resolution determinedfor each area or motion vector by using a motion vector resolutionpredicted using motion vector resolutions of surrounding areas of eacharea, may encode the motion vector resolution determined for each areaor motion vector by using the run and length or may hierarchicallyencode the motion vector resolutions by using a tag tree, or may performthe encoding while changing the number of bits allocated to the motionvector resolution according to the frequency of the motion vectorresolution determined for each area or motion vector. Also, the videoencoding apparatus 900 may determine whether a video decoding apparatuscan estimate the motion vector resolution determined for each area ormotion vector according to a pre-promised estimation scheme, and thenencode an identifier indicating the capability of estimation for an areahaving a motion vector resolution that can be estimated or encode anidentifier indicating the incapability of estimation for an area havinga motion vector resolution that cannot be estimated. In the case wherethe video encoding apparatus 900 hierarchically encodes the motionvector resolutions in a Quadtree structure or by using a tag tree, thevideo encoding apparatus 900 may encode an identifier, which indicatesthe size of an area indicated by the lowest node of the tag tree layersand the maximum number of the tag tree layers or the size of an areaindicated by the lowest node of the Quadtree layers and the maximumnumber of the Quadtree layers, and then include the encoded identifierin a header.

Further, when the size of the differential motion vector or predictedmotion vectors of the motion vector according to the motion vectorresolution determined for each area is larger than a threshold, thevideo encoding apparatus 900 may determine a predetermined value or acertain value as the motion vector resolution determined for each area.Further, when each component of the differential motion vector is “0”,the video encoding apparatus 900 may dispense with encoding theresolution of the motion vector or area.

Further, the video encoding apparatus 900 may encode a differentialmotion vector corresponding to a difference between a predicted motionvector and a motion vector according to the motion vector resolutiondetermined for each area or motion vector. In this event, the videoencoding apparatus 900 may differently encode the differential motionvector depending on the motion vector resolution. To this end, when thevideo encoding apparatus 900 encodes the differential vector by usingthe UVLC, the video encoding apparatus 900 may use the K-th orderExp-Golomb code in the encoding. In this event, the video encodingapparatus 900 may change the degree of order (K) of the Exp-Golomb codeaccording to the motion vector resolution determined for each area.Further, when the video encoding apparatus 900 encodes the differentialvector by using the CABAC, the video encoding apparatus 900 may use theConcatenated Truncated Unary/K-th Order Exp-Golomb Code in the encoding.In the encoding, the video encoding apparatus 900 may change the degreeof order (K) and the maximum value (T) of the Concatenated TruncatedUnary/K-th Order Exp-Golomb Code according to the motion vectorresolution determined for each area. In addition, when the videoencoding apparatus 900 encodes the differential vector by using theCABAC, the video encoding apparatus 900 may differently calculate theaccumulation probability according to the motion vector resolutiondetermined for each area.

Further, the video encoding apparatus 900 may predict a predicted motionvector for a motion vector of each area by using motion vectors ofsurrounding areas of each area. In this event, when the motion vectorresolution of each area is not equal to the motion vector resolution ofsurrounding areas, the video encoding apparatus 900 may perform theprediction after converting the motion vector resolution of thesurrounding areas to the motion vector resolution of said each area.

In addition, the video encoding apparatus 900 may use different methodsof encoding a resolution identification flag according to thedistribution of the motion vector resolutions of surrounding areas ofeach area with respect to the motion vector resolution determinedaccording to each area or motion vector.

Further, in performing the entropy encoding by an arithmetic encoding,the video encoding apparatus 900 uses different methods of generating abit string of a resolution identification flag according to thedistribution of the motion vector resolutions of the surrounding areasof each area and applies different context models according to thedistribution of the motion vector resolutions of the surrounding areasand the probabilities of the motion vector resolution having occurred upto the present, for the arithmetic encoding and probability update.Also, the video encoding apparatus 900 uses different context modelsaccording to the bit position for the arithmetic encoding and contextmodel update.

Moreover, when the block mode of one or more areas among the areas is askip mode, the video encoding apparatus 900 may convert the motionvector resolution of the area of the motion vector to be predicted tothe highest resolution among the motion vector resolutions ofsurrounding areas of the area and then perform the prediction.

FIG. 32 is a block diagram illustrating a video encoding apparatus 3200using an adaptive motion vector according to the second aspect of thepresent disclosure.

A video encoding apparatus 3200 using an adaptive motion vectoraccording to the second aspect of the present disclosure includes aninter prediction encoder 3210, a resolution appointment flag generator3220, a resolution determiner 3230, a resolution encoder 3240, adifferential vector encoder 3250, and a resolution conversion flaggenerator 3260. Meanwhile, it is not inevitably required that all of theresolution appointment flag generator 3220, resolution encoder 3240, thedifferential vector encoder 3250, and the resolution conversion flaggenerator 3260 should be included in the video encoding apparatus 3200,and they may be selectively included in the video encoding apparatus3200.

The inter prediction encoder 3210 performs an inter prediction encodingof a video in the unit of areas of the image by using a motion vectoraccording to a motion vector resolution determined for each motionvector or each area of the video. The inter prediction encoder 3210 canbe implemented by the video encoding apparatus 100 described above withreference to FIG. 1 .

In this event, when one or more elements between the resolution encoder3240 and the differential vector encoder 3250 of FIG. 32 areadditionally included and the function of the additionally includedelement or elements overlaps with the function of the encoder 150 withinthe inter prediction encoder 3210, the overlapping function may beomitted in the encoder 150. Further, if there is an overlapping areabetween the function of the predictor 110 within the inter predictionencoder 3210 and the function of the resolution determiner 3230, theoverlapping function may be omitted in the predictor 110.

Further, one or more elements between the resolution encoder 3240 andthe differential vector encoder 3250 may be configured either as anelement separate from the inter prediction encoder 3210 as shown in FIG.32 or as an element integrally formed with the encoder 150 within theinter prediction encoder 3210. Further, the flag information generatedin the resolution appointment flag generator 3220 or the resolutionconversion flag generator 3260 may be transformed into a bitstreameither by the resolution appointment flag generator 3220 or theresolution conversion flag generator 3260 or by the encoder 150 withinthe inter prediction encoder 3210.

Meanwhile, the functions of the inter prediction encoder 3210, theresolution encoder 3240, and the differential vector encoder 3250 may beequal or similar to those of the inter prediction encoder 910, theresolution encoder 940, and the differential vector encoder 950 in FIG.9 . Therefore, a detailed description on the inter prediction encoder3210, the resolution encoder 3240, and the differential vector encoder3250 is omitted here.

The resolution appointment flag generator 3220 may differently appointthe adaptability degree of the resolution according to each area ormotion vector of a video. The resolution appointment flag generator 3220may generate a resolution appointment flag appointing a set of motionvector resolutions and/or differential motion vector resolutions to eacharea or motion vector of a video, and then include the generatedresolution appointment flag in a bitstream. The area using theresolution appointment flag to indicate a motion vector resolutionand/or differential motion vector resolution may be a block, amacroblock, a group of blocks, a group of macroblocks, or an area havinga predetermined size, such as M×N. That is, the resolution appointmentflag generator 3220 may generate a resolution appointment flagindicating a resolution available for lower areas within some areas of avideo or all areas of the video, and then include the generatedresolution appointment flag in a bitstream. Such a resolutionappointment flag may be determined and generated either according toconfiguration information input by a user or according to apredetermined determination criteria based on an analysis of the videoto be encoded. The resolution appointment flag may be included in aheader of a bitstream, such as a picture parameter set, a sequenceparameter set, or a slice header.

If the resolution appointment flag appoints ½ and ¼ as the resolutionoptions, the optimum resolution determined by the resolution determiner3230 and the resolution identification flag encoded by the resolutionencoder 3240 are selected from the resolutions of ½ and ¼ and theresolution identification flag may be encoded according to apredetermined method. FIG. 33 illustrates resolution identificationflags in the case in which the appointed resolutions are ½ and ¼.

Further, the resolution identification flag may be encoded using a unarycoding, a CABAC, or a Quadtree coding. For example, in the case of usingthe CABAC, a bit string may be first generated using the table shown inFIG. 33 and then subjected to an arithmetic and probability encoding.For example, according to the motion vector resolutions of surroundingmotion vectors or blocks, the context models may be divided into threecases. FIG. 34 illustrates current block X and its surrounding blocks A,B, and C, and FIG. 35 illustrates a context model according to theconditions.

If the resolution appointment flag appoints ½, ¼, and ⅛ as theresolution options, the encoded resolution identification flag may beselected from the resolutions of ½, ¼, and ⅛ and the resolutionidentification flag may be encoded according to a predetermined method.FIG. 36 illustrates resolution identification flags in the case in whichthe appointed resolutions are ½, ¼, and ⅛. Referring to FIG. 36 , theresolution identification flag may be 0, 10, or 11.

The resolution identification flag may be encoded using a unary coding,a CABAC, or a Quadtree coding. For example, in the case of using theCABAC, a bit string may be first generated using the table shown in FIG.36 and then subjected to an arithmetic and probability encoding. Forexample, using the index of bin string and the motion vector resolutionsof surrounding motion vectors or blocks, the context models may bedivided into a total of six cases. In this event, based on FIG. 34illustrating current block X and its surrounding blocks A, B, and C,FIG. 37 illustrates a context model according to the conditions.

In the meantime, the resolution appointment flag generated by theresolution appointment flag generator 3220 may indicate a singleresolution. For example, in the case of fixing the resolution to ½instead of adaptively applying the resolution, the resolutionidentification flag may be encoded to indicate that the resolution ofthe corresponding area is fixed to the resolution of ½.

Further, in the case of using multiple reference pictures, theadaptability degrees (i.e. resolution set) of the resolution may be setto be different according to the reference picture based on apredetermined criterion without encoding the resolution identificationflag. For example, different adaptability degrees of the resolution maybe employed according to the distance between the current picture andreference pictures.

FIGS. 38 and 39 illustrate examples of adaptability degrees according todistances between the current picture and reference pictures. As notedfrom FIG. 38 , when the distance between the current picture and areference picture is nearest (i.e. smallest) among the distances betweenthe current picture and the multiple reference pictures, an optimumresolution may be selected from the resolution set including 1/1, ½, ¼,and ⅛ and a resolution identification flag may be encoded. When thedistance between the current picture and a reference picture is farthest(i.e. largest) among the distances between the current picture and themultiple reference pictures, an optimum resolution may be selected fromthe resolution set including ½ and ¼ and a resolution identificationflag may be encoded. When the distance between the current picture and areference picture is neither nearest (i.e. smallest) nor farthest (i.e.largest) among the distances between the current picture and themultiple reference pictures, an optimum resolution may be selected fromthe resolution set including ½, ¼, and ⅛ and a resolution identificationflag may be encoded. It is noted from FIG. 39 that it is possible to usea single resolution.

Further, at the time of generating reference pictures, differentadaptability degrees of the resolution may be employed using an errormeasurement means, such as a Sum of Squared Difference (SSD) betweenresolutions. For example, if usable resolutions are 1/1, ½, ¼, and ⅛, ininterpolating a reference picture, it is possible to set the resolutionof ½ to be used only when an error value obtained using an errormeasurement means, such as an SSD, for the resolutions of 1/1 and ½exceeds a predetermined threshold while setting the resolution of ½ notto be used when the error value does not exceed the predeterminedthreshold. Further, when it has been set that the resolution of ½ shouldnot be used, it is determined whether an error value obtained using anerror measurement means, such as an SSD, for the resolutions of 1/1 and¼ exceeds a predetermined threshold. When the error value for theresolutions of 1/1 and ¼ does not exceed the predetermined threshold,the resolution of ¼ is set not to be used. In contrast, when the errorvalue for the resolutions of 1/1 and ¼ exceeds the predeterminedthreshold, the resolutions of both 1/1 and ¼ are set to be used. Also,when the resolution of ¼ has been set to be used, it is determinedwhether an error value obtained using an error measurement means, suchas an SSD, for the resolutions of ¼ and ⅛ exceeds a predeterminedthreshold. When the error value for the resolutions of ¼ and ⅛ does notexceed the predetermined threshold, the resolution of ⅛ is set not to beused. In contrast, when the error value for the resolutions of ¼ and ⅛exceeds the predetermined threshold, all the resolutions of 1/1, ¼, and⅛ are set to be used. The threshold may be different according to theresolutions or quantized parameters, or may be the same.

Further, it is possible to encode the employment of differentadaptability degrees of the resolution according to the referencepictures. For example, in the case of using three reference pictures, itis possible to store different index numbers (resolution set indexes inFIG. 9 , which may be reference picture numbers) according topredetermined resolution sets in a header and then transmit them to adecoding apparatus.

FIG. 41 illustrates an example of a structure for encoding of referencepictures.

Meanwhile, the resolution appointment flag generator 3220 may usedifferent resolution sets for a picture to be used as a referencepicture and a picture not to be used as a reference picture,respectively. For example, it is assumed that reference pictures havebeen encoded with the structure as shown in FIG. 41 , and pictures oftime layers TL0, TL1, and TL2 correspond to pictures used as referencepictures while pictures of time layer TL3 correspond to pictures notused as reference pictures. In this event, when the resolution set hasbeen appointed to ½ and ¼ by the resolution appointment flag generator3220, the resolution sets according to the reference pictures may bearranged as shown in FIG. 42 .

Referring to FIG. 42 , the resolution sets at the time of encodingpicture No. 6 are ½ and ¼, and the resolution identification flag orresolution appointment flag may be encoded in the unit of areas ormotion vectors for the resolution sets determined as described above. Atthe time of encoding picture No. 9, the resolution is a singleresolution and it is not required to encode the resolutionidentification flag or resolution appointment flag.

Meanwhile, the resolution appointment flag generator 3220 may includeall functions of the resolution change flag generator 920 as describedabove with reference to FIG. 9 .

The resolution conversion flag generator 3260 generates a resolutionconversion flag, which indicates a change (or difference) between aresolution of an area to be currently encoded and a resolution ofsurrounding areas or a previous resolution.

FIG. 43 illustrates an example of a resolution of a current block andresolutions of surrounding blocks.

For example, when a resolution set includes ½, ¼, and ⅛ and resolutionsof surrounding blocks and a current optimum resolution have values asshown in FIG. 43 , the resolutions of the surrounding blocks are (⅛, ¼,¼, and ¼) and the resolution having the highest frequency is ¼. Further,since the optimum resolution of current block X is also ¼, theresolution conversion flag is encoded to “0”. In this event, the decodercan extract the resolution conversion flag from a bitstream. Also, whenthe resolution conversion flag is 0, the decoder can obtain informationthat the resolution having the highest frequency, ¼, is the resolutionof current block X.

FIG. 44 illustrates another example of a resolution of a current blockand resolutions of surrounding blocks, and FIG. 45 illustratesresolution identification flags according to resolutions.

In FIG. 44 , since the optimum resolution of current block X is not ¼,which is the resolution of the surrounding block having the highestfrequency among the resolutions of the surrounding blocks, theresolution conversion flag is encoded to 1 so as to indicate that it isa resolution different from those of the surrounding blocks, and theresolution identification flag of the resolution of current block X isencoded to 1 by using the table shown in FIG. 45 . Since there is nopossibility that ¼ is selected as the converted resolution when thecurrent resolution is ¼, a resolution identification flag is notprovided in the case of the resolution of ¼.

FIG. 46 illustrates an example of the resolution of the current blockand the resolutions of surrounding blocks.

For example, when a resolution set includes ½ and ¼ and the encoding hasbeen performed as shown in FIG. 46 , since a previous block of currentblock X is A, the resolution conversion flag may indicate whether theresolution of block A and the resolution of current block X areidentical to each other. Therefore, in the case described above, theresolution of block A and the resolution of current block X are notidentical to each other, and the resolution conversion flag may thushave a value of 1. Further, since the resolution set includes ½ and ¼,it is possible to understand that the resolution of the current block is¼, even with only the resolution conversion flag without additionallyencoding the resolution identification flag.

FIG. 47 is a flowchart illustrating a video encoding method using anadaptive motion vector resolution according to the second aspect of thepresent disclosure.

As shown in FIG. 47 , the video encoding method using an adaptive motionvector resolution according to the second aspect of the presentdisclosure includes: a resolution appointment flag generating step(S4702), a resolution determining step (S4704), an inter predictionencoding step (S4706), a differential vector encoding step (S4708), aresolution encoding step (S4710), and a resolution conversion flaggenerating step (S4712).

The resolution appointment flag generating step (S4702) corresponds tothe operation of the resolution appointment flag generator 3220, aresolution determining step (S4704) corresponds to the operation of theresolution determiner 3230, an inter prediction encoding step (S4706)corresponds to the operation of the inter prediction encoder 3210, adifferential vector encoding step (S4708) corresponds to the operationof the differential vector encoder 3250, a resolution encoding step(S4710) corresponds to the operation of the resolution encoder 3240, anda resolution conversion flag generating step (S4712) corresponds to theoperation of the resolution conversion flag generator 3260. Therefore, adetailed description on the process in each step is omitted here.

Further, the steps described above may include a step or steps, whichcan be omitted, depending on the existence or absence of each element ofthe video encoding apparatus 3200, from the method of encoding a videousing an adaptive motion vector resolution according to the secondaspect of the present disclosure.

FIG. 18 is a block diagram illustrating a video decoding apparatus usingan adaptive motion vector according to the first aspect of the presentdisclosure.

The video decoding apparatus 1800 using an adaptive motion vectoraccording to the first aspect of the present disclosure includes aresolution change flag extractor 1810, a resolution decoder 1820, adifferential vector decoder 1830, and an inter prediction decoder 1840.

The resolution change flag extractor 1810 extracts a resolution changeflag from a bitstream. That is, the resolution change flag extractor1810 extracts a resolution change flag, which indicates whether themotion vector resolution is fixed or changes according to each area,from a header of a bitstream. When the resolution change flag indicatesthat the motion vector resolution is fixed, the resolution change flagextractor 1810 extracts an encoded motion vector resolution from thebitstream and then decodes the extracted motion vector resolution, so asto make the inter prediction decoder 1840 perform an inter predictiondecoding of all lower areas defined in the header with the reconstructedfixed motion vector resolution or a preset motion vector resolution andmake the differential vector decoder 1830 reconstruct a motion vector ofeach area with the fixed motion vector. When the resolution change flagindicates that the motion vector resolution changes according to eacharea or motion vector, the resolution change flag extractor 1810 causesthe resolution decoder 1820 to reconstruct a motion vector resolution ofeach lower area or motion vector defined in the header, causes the interprediction decoder 1840 to perform an inter prediction decoding of eachlower area or motion vector defined in the header with the reconstructedmotion vector resolution, and causes the differential vector decoder1830 to reconstruct a motion vector of each area with the reconstructedmotion vector.

Further, when the size of a predicted motion vector or differentialmotion vector of a motion vector according to a motion vector resolutiondetermined for each area or motion vector is larger than a threshold,the resolution change flag extractor 1810 may determine a predeterminedvalue as the motion vector resolution of each area or motion vector. Forexample, when the size of a differential motion vector or the size of apredicted motion vector of an area or a motion vector is larger than athreshold, the resolution change flag extractor 1810 may determine apredetermined value as a motion vector resolution of the area or themotion vector without decoding the motion vector resolution of the area.Further, when the size of a motion vector of a surrounding area of anarea or a motion vector is larger or the size of a motion vector of anarea is larger than a threshold, the resolution change flag extractor1810 may determine a predetermined value as a motion vector resolutionof the area without decoding the motion vector resolution of the area.In this event, the motion vector resolution of the area or motion vectorcan be changed to a predetermined resolution even without a flag. Thethreshold may be a pre-appointed value or a certain input value, or maybe calculated from a motion vector of a surrounding block.

The resolution decoder 1820 extracts an encoded resolutionidentification flag from a bitstream according to a resolution changeflag extracted by the resolution change flag extractor 1810 and decodesthe extracted resolution identification flag, so as to reconstruct themotion vector resolution of each area. Meanwhile, a decoding of a motionvector resolution by the resolution decoder 1820 simply described forconvenience in the following discussion may actually include a decodingof one of or both of a motion vector resolution and a differentialmotion vector. Therefore, the resolution indicated by the resolutionidentification flag may be either a resolution of a motion vector or aresolution of a differential motion vector, or may indicate both aresolution of a motion vector and a resolution of a differential motionvector.

To this end, the resolution change flag extractor 1810 may reconstruct amotion vector resolution of each area or motion vector by decoding aresolution identification flag hierarchically encoded in a Quadtreestructure by grouping areas having the same motion vector resolutiontogether.

Referring to FIGS. 10 to 12 , the resolution decoder 1820 reconstructsthe motion vector resolutions by decoding the resolution identificationflags with a Quadtree structure as shown in FIG. 10 according to theareas as shown in FIG. 12 . For example, in the case of decoding theresolution identification flag generated through the encoding as shownin FIG. 11 , the first bit has a value of “1”, which implies a divisioninto sub layers, and the second bit has a value of “0”, which impliesthat the first node of level 1 has not been divided into sub layers.Therefore, by decoding the next bits, a motion vector resolution of ½isreconstructed. In the same manner as described above, the resolutionidentification flags for level 1 and level 2 are decoded in the samemanner as, but in a reverse order to, the encoding method as describedabove with reference to FIGS. 10 and 11 , so as to reconstruct theresolution identification flags of the corresponding areas or motionvectors. Further, since an identifier indicating the size of an areaindicated by the lowest node and the maximum number of layers includedin a header defines that the maximum number of layers in level 3 shouldbe 3, the resolution decoder 1820 determines that there are no morelayers lower than level 3, and then reconstructs only the motion vectorresolution of each area. To this end, the resolution decoder 1820decodes an identifier, which indicates the size of the area indicated bythe lowest node of Quadtree layers and the maximum number of Quadtreelayers and is included in a header of a bitstream.

Although the above description discusses only two examples including anexample in which a node is divided into lower layers (i.e. four areas)and another example in which a node is not divided into lower layers.There may be various cases as shown in FIG. 20 , including a case inwhich a node is not divided into lower layers and cases in which a nodeis divided into lower layers in various ways, for example, a node may bedivided into two transversely lengthy areas, two longitudinally lengthyareas, or four areas.

Further, the resolution decoder 1820 may reconstruct the motion vectorresolution of each area or motion vector by decoding the resolutionidentification flag encoded using a predicted motion vector resolutionpredicted by motion vector resolutions of surrounding areas of the areaor motion vector. For example, when the resolution identification flagextracted for each area or motion vector from a bitstream indicates thatits resolution is identical to a motion vector resolution predictedusing motion vector resolutions of surrounding areas (e.g. when the bitvalue of the resolution identification flag is “1”), the resolutiondecoder 1820 may reconstruct the motion vector resolution predictedusing motion vector resolutions of surrounding areas without reading thenext resolution identification flag from the bitstream. In contrast,when the resolution identification flag indicates that its resolution isnot identical to the motion vector resolution predicted using motionvector resolutions of surrounding areas (e.g. when the bit value of theresolution identification flag is “0”), the resolution decoder 1820 mayreconstruct the motion vector resolution by reading the next resolutionidentification flag from the bitstream and decoding the next resolutionidentification flag.

In addition, the resolution decoder 1820 may reconstruct the motionvector resolution of each area or motion vector by decoding theresolution identification flag of the motion vector resolution having anencoded run and length. For example, the resolution decoder 1820 mayreconstruct the run and length of the motion vector resolution bydecoding the encoded resolution identification flag of the differentialmotion vector resolutions and/or motion vector resolutions of a part ofmultiple areas, or may reconstruct the motion vector resolutions of theareas as shown in FIG. 12 by using the reconstructed run and length ofthe motion vector resolution.

Moreover, the resolution decoder 1820 may reconstruct the motion vectorresolution of each area or motion vector by decoding the resolutionidentification flag hierarchically encoded using a tag tree. Referringto FIGS. 13 and 14 as an example, since one can see from the bit of thefirst area shown in FIG. 1 , which is “0111”, that the bitscorresponding to level 0 are “01” and it is assumed that the number ofthe motion vector resolution of a higher level of level 0 is “0”, theresolution decoder 1820 may reconstruct the motion vector resolution of½, which has a resolution number difference value of 1 from a higherlevel. Further, since the next bit is “1”, which has a resolution numberdifference value of “0” from a higher layer, ½ is reconstructed as themotion vector resolution in level 1 also. Also, since each of thefollowing bits is also “1”, ½ is reconstructed as the motion vectorresolution in level 2 and level 3 also, respectively. Since the bits ofthe second area in FIG. 14 are “01” and the motion vector resolutions oflevel 0, level 1, and level 2 in the first area have been alreadydecoded, a decoding of the motion vector resolution of only level 3 isrequired. In level 3, since the resolution number difference value froma higher layer is “1”, it is possible to reconstruct a motion vectorresolution of ¼. In the same manner, motion vector resolutions of theother areas can be reconstructed.

Further, the resolution decoder 1820 may change and decode the number ofbits allocated to the resolution identification flag according to theoccurrence frequency of the motion vector resolution determined for eachmotion vector or area. For example, the resolution decoder 1820 maycalculate the occurrence frequency of the reconstructed motion vectorresolution up to the just previous area, provide numbers to motionvector resolutions according to the calculated occurrence frequency, andallocate bit numbers according to the provided numbers, so as to decodethe motion vector resolutions.

The area group may be a Quadtree, a Quadtree bundle, a tag tree, a tagtree bundle, a macroblock, a macroblock bundle, or an area with apredetermined size. For example, when the area group is appointed asincluding two macroblocks, it is possible to update the occurrencefrequency of the motion vector resolution for every two macroblocks andallocate a bit number of the motion vector resolution to the updatedfrequency, for the decoding. Otherwise, when the area group is appointedas including four Quadtrees, it is possible to update the occurrencefrequency of the motion vector resolution for every four Quadtrees andallocate a bit number of the motion vector resolution to the updatedfrequency, for the decoding.

Further, the resolution decoder 1820 may use different methods fordecoding a resolution identification flag according to the distributionof the motion vector resolutions of surrounding areas of each area withrespect to the motion vector resolution determined according to eacharea or motion vector. That is, the smallest bit number is allocated toa resolution having the highest probability that the resolution may bethe resolution of a corresponding area according to the distribution ofthe motion vector resolutions of surrounding areas or area groups. Forexample, if a left side area of the corresponding area has a motionvector resolution of ½ and an upper side area of the area has a motionvector resolution of ½, it is most probable that the area may have amotion vector resolution of ½, and the smallest bit number is thusallocated to the motion vector resolution of ½, which is then decoded.As another example, if a left side area of the corresponding area has amotion vector resolution of ¼, a left upper side area of the area has amotion vector resolution of ½, an upper side area of the area has amotion vector resolution of ½, and a right upper side area of the areahas a motion vector resolution of ½, the bit numbers are allocated tothe motion vector resolutions in a sequence causing the smaller bitnumber to be allocated to a motion vector resolution having the higherprobability, for example, in a sequence of ½, ¼, ⅛, . . . , and themotion vector resolutions are then decoded.

Further, in performing the entropy decoding by an arithmetic decoding,the resolution decoder 1820 uses different methods of generating a bitstring of a resolution identification flag according to the distributionof the motion vector resolutions of the surrounding areas of each areafor the motion vector resolution determined according to each motionvector or area and applies different context models according to thedistribution of the motion vector resolutions of the surrounding areasand the probabilities of the motion vector resolution having occurred upto the present, for the arithmetic decoding and probability update.Further, in the arithmetic decoding and probability update, theresolution decoder 1820 may use different context models according tothe positions of bits. For example, based on an assumption that anentropy decoding is performed using only three motion vector resolutionsincluding ½, ¼, and ⅛ by the CABAC, if a left side area of a pertinentarea has a motion vector resolution of ½ and an upper side area of thearea has a motion vector resolution of ½, the shortest bit string (“0”in FIG. 21 ) is allocated to the motion vector resolution of ½ and theother bit strings are allocated to the other motion vector resolutions,i.e. ¼ and ⅛, in a sequence causing the smaller bit number to beallocated to a motion vector resolution having the higher probability.

In this event, if the motion vector resolution of ⅛ has the higheroccurrence probability up to the present than that of the motion vectorresolution of ¼, the bitstream of “00” is allocated to the motion vectorresolution of ⅛ and the bitstream of “01” is allocated to the motionvector resolution of ½. Further, in decoding the first bit string, fourdifferent context models may be used, which include: a first contextmodel in which the resolution of the left side area is equal to theresolution of the upper side area, which is equal to the resolution ofthe highest probability up to the present; a second context model inwhich the resolution of the left side area is equal to the resolution ofthe upper side area, which is different from the resolution of thehighest probability up to the present; a third context model in whichthe resolutions of the left side area and the upper side area aredifferent from each other and at least one of the resolutions of theleft side area and the upper side area is equal to the resolution of thehighest probability up to the present; and a fourth context model inwhich the resolutions of the left side area and the upper side area aredifferent from each other and neither of them is equal to the resolutionof the highest probability up to the present. In decoding the second bitstring, two different context models may be used, which include: a firstcontext model in which the resolutions of the left side area and theupper side area are different from each other and at least one of theresolutions of the left side area and the upper side area is equal tothe resolution of the highest probability up to the present; and asecond context model in which the resolutions of the left side area andthe upper side area are different from each other and neither of them isequal to the resolution of the highest probability up to the present.

As another example, based on an assumption that an entropy decoding isperformed using only three motion vector resolutions including ½, ¼, and⅛ by the CABAC and the highest motion vector resolution up to thepresent is ¼, “1”, which is the shortest bitstream, is allocated to themotion vector resolution of ¼, and “00” and “01” are then allocated tothe other motion vector resolutions of ½ and ⅛, respectively.

Further, in decoding the first bit string, three different contextmodels may be used, which include: a first context model in which eachof the resolutions of the left side area and the upper side area of acorresponding area is equal to the resolution of the highest probabilityup to the present; a second context model in which only one of theresolutions of the left side area and the upper side area of acorresponding area is equal to the resolution of the highest probabilityup to the present; and a third context model in which neither of theresolutions of the left side area and the upper side area of acorresponding area is equal to the resolution of the highest probabilityup to the present. In decoding the second bit string, six differentcontext models may be used, which include: a first context model inwhich each of the resolution of the left side area and the resolution ofthe upper side area of a corresponding area corresponds to a motionvector resolution of ⅛; a second context model in which each of theresolutions of the left side area and the upper side area of acorresponding area corresponds to a motion vector resolution of ½; athird context model in which each of the resolutions of the left sidearea and the upper side area of a corresponding area corresponds to amotion vector resolution of ¼; a fourth context model in which one ofthe resolutions of the left side area and the upper side area of acorresponding area corresponds to a motion vector resolution of ⅛ andthe other resolution corresponds to a motion vector resolution of ¼; afifth context model in which one of the resolutions of the left sidearea and the upper side area of a corresponding area corresponds to amotion vector resolution of ½ and the other resolution corresponds to amotion vector resolution of ¼; and a sixth context model in which one ofthe resolutions of the left side area and the upper side area of acorresponding area corresponds to a motion vector resolution of ⅛ andthe other resolution corresponds to a motion vector resolution of ½. Theresolution of the highest probability up to the present may be aprobability of a resolution encoded up to the previous area, aprobability of a certain area, or a predetermined fixed resolution.

Further, when the resolution identification flag decoded for each areaor motion vector is a flag indicating the capability of estimation, theresolution decoder 1820 may estimate a motion vector resolutionaccording to a pre-promised estimation scheme, so as to reconstruct theestimated motion vector resolution as a motion vector resolution of thearea or motion vector. In contrast, when the resolution identificationflag decoded for each area or motion vector is a flag indicating theincapability of estimation, the resolution decoder 1820 may reconstructthe motion vector resolution indicated by the decoded resolutionidentification flag as the motion vector of the area.

For example, when the resolution identification flag decoded for eacharea or motion vector indicates the capability of estimation, theresolution decoder 1820 predicts a predicted motion vector by changingeach decoded motion vector resolution in a method equal or similar tothe method of the video encoding apparatus 900, and reconstructs amotion vector by using the predicted motion vector and a differentialmotion vector reconstructed by the differential vector decoder 1830.First, based on an assumption that a motion vector resolution of apredetermined area corresponds to a ¼ pixel unit, when the predictedmotion vector is (3, 14), the differential motion vector is (2, 3) andthe reconstructed motion vector of the predetermined area is thus (5,17). Based on an assumption that a motion vector resolution of apredetermined area corresponds to a ½ pixel unit, when the predictedmotion vector is (2, 7), the reconstructed differential motion vector is(2, 3) and the reconstructed motion vector of the predetermined area isthus (4, 10). A resolution having the least distortion betweensurrounding pixels of a pertinent area and surrounding pixels of an areamotion-compensated using a reconstructed motion vector of eachresolution in a reference picture is an optimum motion vectorresolution. Therefore, when surrounding pixels of an areamotion-compensated in the unit of ½ pixels has the least distortion, themotion vector resolution of ½ is the optimum motion vector resolution.

Further, when the resolution identification flag decoded for each areaor motion vector indicates the capability of estimation, the resolutiondecoder 1820 may reconstruct the motion vector resolution of thepertinent area or motion vector by additionally decoding the motionvector resolution in the resolution identification flag.

Further, the resolution decoder 1820 can reconstruct the motion vectorresolution of each area or motion vector only when each component of thedifferential motion vector is not “0”. That is, when a component of adifferential motion vector of a particular area is “0”, the resolutiondecoder 1820 may decode a predicted motion vector into a motion vectorwithout reconstructing the motion vector resolution of the particulararea.

The differential vector decoder 1830 extracts an encoded differentialmotion vector from a bitstream and decodes the extracted differentialmotion vector. Specifically, the differential vector decoder 1830reconstructs the differential motion vector of each area or motionvector by performing the decoding according to the motion vectorresolution of each reconstructed area or motion vector. Additionally,the inter prediction decoder 1840 may predict a predicted motion vectorof each area and reconstruct a motion vector of each area by using thepredicted motion vector and the reconstructed differential motionvector.

To this end, the differential vector decoder 1830 may use UVLC indecoding the differential motion vector. In this event, the differentialvector decoder 1830 may use the K-th order Exp-Golomb code in thedecoding and may change the degree of order (K) of the Exp-Golomb codeaccording to the motion vector resolution determined for eachreconstructed area. Further, the differential vector decoder 1830 maydecode the differential vector by using the CABAC. In this event, thedifferential vector decoder 1830 may use the Concatenated TruncatedUnary/K-th Order Exp-Golomb Code in the decoding and may change thedegree of order (K) and the maximum value (T) of the ConcatenatedTruncated Unary/K-th Order Exp-Golomb Code according to the motionvector resolution determined for each reconstructed area or motionvector. In addition, when the differential vector decoder 1830 decodesthe differential vector by using the CABAC, the differential vectordecoder 1830 may differently calculate the accumulation probabilityaccording to the motion vector resolution determined for eachreconstructed area or motion vector.

Further, the differential vector decoder 1830 may predict a predictedmotion vector for each area or motion vector by using motion vectors ofsurrounding areas of each area or motion vector. In this event, when themotion vector resolution of each area is not equal to the motion vectorresolution of surrounding areas, the differential vector decoder 1830may convert the motion vector resolution of the surrounding areas to themotion vector resolution of said each area for the prediction. Thepredicted motion vector can be obtained in the same method by the videoencoding apparatus and the video decoding apparatus. Therefore, variousaspects for the motion vector resolution conversion and for obtaining apredicted motion vector by a video encoding apparatus as described abovewith reference to FIGS. 22 to 26 can also be applied to a video decodingapparatus according to the following aspects of the present disclosure.

Further, when at least one area among the areas is a block and the blockmode of the block is a skip mode, the differential vector decoder 1830may convert motion vector resolutions of surrounding areas of the areato the highest resolution among the motion vector resolutions of thesurrounding areas and then perform the prediction.

Moreover, the resolution identification flag indicating the motionvector resolution decoded by the resolution decoder 1820 may indicateeither both or each of the resolutions of an x component and a ycomponent of a motion vector. That is, when a camera taking a videomoves or when an object within a video moves, the resolution decoder1820 may perform the decoding with different resolutions for the xcomponent and the y component of a motion vector for motion estimation.For example, the resolution decoder 1820 may perform the decoding with aresolution of ⅛ pixel unit for the x component of a motion vector of acertain area while performing the decoding with a resolution of ½ pixelunit for the y component of the motion vector. Then, the interprediction decoder 1840 may perform an inter prediction decoding of apertinent area by performing a motion estimation and a motioncompensation of a motion vector of the pertinent area by using differentresolutions for the x component and the y component of the motionvector. The inter prediction decoder 1840 performs an inter predictiondecoding of each area by using a motion vector of each area according tothe motion vector resolution of each reconstructed area or motionvector. The inter prediction decoder 1840 may be implemented by thevideo decoding apparatus 800 described above with reference to FIG. 8 .When functions of the resolution change flag extractor 1810, theresolution decoder 1820, and the differential vector decoder 1830 inFIG. 18 overlap with the function of the decoder 810 of the videodecoding apparatus 800, the overlapping functions may be omitted in thedecoder 810.

Further, when the operation of the resolution decoder 1820 overlaps withthe operation of the predictor 850, the overlapping operation may beomitted in the predictor 850.

Also, the resolution change flag extractor 1810, the resolution decoder1820, and the differential vector decoder 1830 may be constructed eitherseparately from the inter prediction decoder 1840 as shown in FIG. 18 orintegrally with the decoder 810 within the video decoding apparatus1800.

However, although the above description with reference to FIG. 8discusses decoding of a video in the unit of blocks by the videodecoding apparatus 800, the inter prediction decoder 1840 may divide thevideo into areas with various shapes or sizes, such as blocks includingmacroblocks or subblocks, slices, or pictures, and perform the decodingin the unit of areas each having a predetermined size. Such apredetermined area may be not only a macroblock having a size of 16×16but also blocks with various shapes or sizes, such as a block having asize of 64×64 and a block having a size of 32×16.

Further, although the video decoding apparatus 800 described above withreference to FIG. 8 performs an inter prediction decoding using motionvectors having the same motion vector resolution for all blocks of avideo, the inter prediction decoder 1840 may perform an inter predictiondecoding using motion vectors having motion vector resolutionsdifferently determined according to each area or motion vector. That is,in the inter prediction decoding of an area, the inter predictiondecoder 1840 first enhances the resolution of an area by interpolating areference picture having been already encoded, decoded, andreconstructed according to a motion vector resolution and/or adifferential motion vector resolution of each area or motion vectorreconstructed by the resolution decoder 1820, and then performs a motionestimation by using a motion vector and/or a differential motion vectoraccording to the motion vector resolution and/or the differential motionvector resolution of the pertinent area or motion vector reconstructedby the differential vector decoder 1830. For the interpolation of thereference picture, it is possible to use various interpolation filters,such as a Wiener filter, a bilinear filter, and a Kalman filter and toapply resolutions in the unit of various integer pixels or fractionpixels, such as 2 pixel unit, 1 pixel unit, 2/1 pixel unit, 1/1 pixelunit, ½ pixel unit, ¼ pixel unit, and ⅛ pixel unit. Further, accordingto such various resolutions, it is possible to use different filtercoefficients or different numbers of filter coefficients. For example, aWiener filter may be used for the interpolation when the resolutioncorresponds to the ½ pixel unit and a Kalman filter may be used for theinterpolation when the resolution corresponds to the ¼ pixel unit.Moreover, different numbers of taps may be used for the interpolation ofthe respective resolutions. For example, an 8-tap Wiener filter may beused for the interpolation when the resolution corresponds to the ½pixel unit and a 6-tap Wiener filter may be used for the interpolationwhen the resolution corresponds to the ¼ pixel unit.

Further, the inter prediction decoder 1840 may decode the filtercoefficient of each motion vector resolution and then interpolate areference picture with an optimum filter coefficient for each motionvector resolution. In this event, it is possible to use various filtersincluding a Wiener filter and a Kalman filter and to employ variousnumbers of filter taps. Further, it is possible to employ differentnumbers of filters or different numbers of filter taps according to theresolutions of the motion vectors. Moreover, the inter predictiondecoder 1840 may perform the inter prediction decoding by usingreference pictures interpolated using different filters according to themotion vector resolution of each area or motion vector. For example, afilter coefficient of a 6-tap Wiener filter may be decoded for the ½resolution, a filter coefficient of an 8-tap Kalman filter may bedecoded for the ¼ resolution, a filter coefficient of a linear filtermay be decoded for the ⅛ resolution, and the reference picture for eachresolution may be then interpolated and decoded. In the decoding, theinter prediction decoder 1840 may use a reference picture interpolatedby a 6-tap Wiener filter when the resolution of the current area ormotion vector is a ½ resolution, and may use a reference pictureinterpolated by a 8-tap Kalman filter when the resolution of the currentarea or motion vector is a ¼ resolution.

FIG. 48 is a block diagram illustrating a video decoding apparatus usingan adaptive motion vector according to the second aspect of the presentdisclosure.

The video decoding apparatus 4800 using an adaptive motion vectoraccording to the second aspect of the present disclosure includes aresolution appointment flag extractor 4810, a resolution decoder 4820, adifferential vector decoder 4830, an inter prediction decoder 4840, anda resolution conversion flag extractor 4850. In this event, all of theresolution appointment flag extractor 4810, the resolution decoder 4820,the differential vector decoder 4830, and the resolution conversion flagextractor 4850 are not necessarily included in the video decodingapparatus 4800 and may be selectively included in the video decodingapparatus 4800 according to the encoding scheme of a video encodingapparatus for generating an encoded bitstream.

Further, the inter prediction decoder 4840 performs an inter predictiondecoding of each area by using a motion vector of each area according tothe motion vector resolution of each reconstructed area or motionvector. The inter prediction decoder 4840 may be implemented by thevideo decoding apparatus 800 described above with reference to FIG. 8 .When one or more functions of the resolution change flag extractor 4810,the resolution decoder 4820, the differential vector decoder 4830, andthe resolution conversion flag extractor 4850 in FIG. 48 overlap withthe function of the decoder 810 within the video decoding apparatus4800, the overlapping functions may be omitted in the decoder 810.Further, when the operation of the resolution decoder 4820 overlaps withthe operation of the predictor 850 within the inter prediction decoder4840, the overlapping operation may be omitted in the predictor 850.

Also, the resolution change flag extractor 4810, the resolution decoder4820, the differential vector decoder 4830, and the resolutionconversion flag extractor 4850 may be constructed either separately fromthe inter prediction decoder 4840 as shown in FIG. 48 or integrally withthe decoder 810 within the video decoding apparatus 4800.

The resolution appointment flag extractor 4810 extracts a resolutionappointment flag from an input bitstream. The resolution appointmentflag corresponds to a flag indicating that it is fixed to a singleresolution or a resolution set including multiple resolutions.

The resolution appointment flag extractor 4810 extracts a resolutionappointment flag from a bitstream. That is, the resolution appointmentflag extractor 4810 extracts a resolution appointment flag, whichindicates whether the motion vector resolution is fixed to apredetermined value or corresponds to a resolution set includingdifferent resolutions according to areas, from a header of a bitstream.When the resolution appointment flag indicates that the motion vectorresolution and/or differential motion vector resolution is fixed to apredetermined resolution, the resolution appointment flag extractor 4810transmits the fixed resolution indicated by the resolution appointmentflag to the inter prediction decoder 4840 and the differential vectordecoder 4830, and the differential vector decoder 4830 then decodes adifferential motion vector by using the received resolution and thentransmits the decoded differential motion vector to the inter predictiondecoder 4840. Then, the inter prediction decoder 4840 performs an interprediction decoding by using the received differential motion vector,the resolution received from the resolution appointment flag extractor4810, and the received bitstream.

When the resolution appointment flag corresponds to a predeterminedresolution set, the resolution change flag extractor 4810 causes theresolution decoder 4820 to reconstruct a motion vector resolution and/ordifferential motion vector resolution of each lower area or motionvector defined in the header, causes the inter prediction decoder 4840to perform an inter prediction decoding of each lower area or motionvector defined in the header with the reconstructed motion vectorresolution, and causes the differential vector decoder 4830 toreconstruct a motion vector of each area with the reconstructed motionvector.

Further, in the case of using multiple reference pictures, anadaptability degree (i.e. resolution set) of the resolution may becalculated for each reference picture based on a predetermined criterionwhen the resolution appointment flag is not extracted from a bitstream.For example, different adaptability degrees of the resolution may beemployed according to the distance between the current picture andreference pictures. This configuration has been already described abovewith reference to FIGS. 38 and 39 , so a detailed description thereof isomitted here.

Further, at the time of generating reference pictures, the resolutionset may be calculated using an error measurement means, such as a Sum ofSquared Difference (SSD) between resolutions. For example, if usableresolutions are 1/1, ½, ¼, and ⅛, in interpolating a reference picture,it is possible to set the resolution of ½ to be used only when an errorvalue obtained using an error measurement means, such as an SSD, for theresolutions of 1/1 and ½ exceeds a predetermined threshold while settingthe resolution of ½ not to be used when the error value does not exceedthe predetermined threshold. Further, when it has been set that theresolution of ½ should not be used, it is determined whether an errorvalue obtained using an error measurement means, such as an SSD, for theresolutions of 1/1 and ¼ exceeds a predetermined threshold. When theerror value for the resolutions of 1/1 and ¼ does not exceed thepredetermined threshold, the resolution of ¼ is set not to be used. Incontrast, when the error value for the resolutions of 1/1 and ¼ exceedsthe predetermined threshold, the resolutions of both 1/1 and ¼ are setto be used. Also, when the resolution of ¼ has been set to be used, itis determined whether an error value obtained using an error measurementmeans, such as an SSD, for the resolutions of ¼ and ⅛ exceeds apredetermined threshold. When the error value for the resolutions of ¼and ⅛ does not exceed the predetermined threshold, the resolution of ⅛is set not to be used. In contrast, when the error value for theresolutions of ¼ and ⅛ exceeds the predetermined threshold, all theresolutions of 1/1, ¼, and ⅛ are set to be used. The threshold may bedifferent according to the resolutions or quantized parameters, or maybe the same.

Further, in the case of encoding the employment of differentadaptability degrees of the resolution according to the referencepictures, the resolution appointment flag extractor 4810 may extract aresolution set by extracting a reference picture index number instead ofthe resolution appointment flag from the bitstream and then storing andreferring to the reference picture index number corresponding to eachpredetermined resolution set as shown in FIG. 40 .

Also, when the resolution appointment flag indicates a resolution set,it is possible to set an actually usable resolution set according to theuse or non-use of a reference picture by setting different resolutionsets for a picture to be used as a reference picture and a picture notto be used as a reference picture, respectively. Therefore, the videodecoding apparatus 4800 may also store a table as shown in FIG. 42 to bereferred to by the resolution decoder 4820 in decoding the resolution.This configuration also has been already described above with referenceto FIGS. 41 and 42 , so a detailed description thereof is omitted here.

Further, when the size of a predicted motion vector or differentialmotion vector of a motion vector according to a motion vector resolutionand/or differential motion vector resolution determined for each area ormotion vector is larger than a threshold, the resolution appointmentflag extractor 4810 may determine a predetermined value as the motionvector resolution and/or differential motion vector resolutiondetermined for each area or motion vector.

This configuration also has been already described above in thediscussion relating to the resolution change flag extractor 1810 of thevideo decoding apparatus 1800 according to the first aspect, so adetailed description thereof is omitted here.

The resolution decoder 4820 extracts an encoded resolutionidentification flag from a bitstream according to a resolutionappointment flag extracted by the resolution appointment flag extractor4810 and decodes the extracted resolution identification flag, so as toreconstruct the motion vector resolution of each area.

To this end, the resolution appointment flag extractor 4810 mayreconstruct a motion vector resolution of each area or motion vector bydecoding a resolution identification flag hierarchically encoded in aQuadtree structure by grouping areas having the same motion vectorresolution together. This configuration also has been already describedabove in the discussion relating to the resolution change flag extractor1810 of the video decoding apparatus 1800 according to the first aspect,so a detailed description thereof is omitted here.

Further, the resolution decoder 4820 may reconstruct the motion vectorresolution of each area or motion vector by decoding the resolutionidentification flag encoded using a predicted motion vector resolutionpredicted using motion vector resolutions of surrounding areas of thearea or motion vector. This configuration also has been alreadydescribed above in the discussion relating to the resolution change flagextractor 1810 of the video decoding apparatus 1800 according to thefirst aspect, so a detailed description thereof is omitted here.

In addition, the resolution decoder 4820 may reconstruct the motionvector resolution of each area or motion vector by decoding theresolution identification flag of the motion vector resolution having anencoded run and length for each area or motion vector. Thisconfiguration also has been already described above in the discussionrelating to the resolution change flag extractor 1810 of the videodecoding apparatus 1800 according to the first aspect, so a detaileddescription thereof is omitted here.

Moreover, the resolution decoder 4820 may reconstruct the motion vectorresolution of each area or motion vector by decoding the resolutionidentification flag hierarchically encoded using a tag tree. Thisconfiguration also has been already described above in the discussionrelating to the resolution change flag extractor 1810 of the videodecoding apparatus 1800 according to the first aspect, so a detaileddescription thereof is omitted here.

Further, the resolution decoder 4820 may change and decode the number ofbits allocated to the resolution identification flag according to theoccurrence frequency of the motion vector resolution determined for eachmotion vector or area. For example, the resolution decoder 4820 maycalculate the occurrence frequency of the reconstructed motion vectorresolution up to the just previous area, provide numbers to motionvector resolutions according to the calculated occurrence frequency, andallocate bit numbers according to the provided numbers, so as to decodethe motion vector resolutions. This configuration also has been alreadydescribed above in the discussion relating to the resolution change flagextractor 1810 of the video decoding apparatus 1800 according to thefirst aspect, so a detailed description thereof is omitted here.

Further, the resolution decoder 4820 may use different methods fordecoding a resolution identification flag according to the distributionof the motion vector resolutions of surrounding areas of each area withrespect to the motion vector resolution determined according to eacharea or motion vector. That is, the smallest bit number is allocated toa resolution having the highest probability that the resolution may bethe resolution of a corresponding area according to the distribution ofthe motion vector resolutions of surrounding areas or area groups. Thisconfiguration also has been already described above in the discussionrelating to the resolution change flag extractor 1810 of the videodecoding apparatus 1800 according to the first aspect, so a detaileddescription thereof is omitted here.

Further, in performing the entropy decoding by an arithmetic decoding,the resolution decoder 4820 may use different methods of generating abit string of a resolution identification flag according to thedistribution of the motion vector resolutions of the surrounding areasof each area for the motion vector resolution determined according toeach motion vector or area and may apply different context modelsaccording to the distribution of the motion vector resolutions of thesurrounding areas and the probabilities of the motion vector resolutionhaving occurred up to the present, for the arithmetic decoding andprobability update. Further, in the arithmetic decoding and probabilityupdate, the resolution decoder 4820 may use different context modelsaccording to the positions of bits. This configuration also has beenalready described above in the discussion relating to the resolutionchange flag extractor 1810 of the video decoding apparatus 1800according to the first aspect, so a detailed description thereof isomitted here.

Further, when the resolution identification flag decoded for each areaor motion vector is a flag indicating the capability of estimation, theresolution decoder 4820 may estimate a motion vector resolutionaccording to a pre-promised estimation scheme, so as to reconstruct theestimated motion vector resolution as a motion vector resolution of thearea or motion vector. In contrast, when the resolution identificationflag decoded for each area or motion vector is a flag indicating theincapability of estimation, the resolution decoder 4820 may reconstructthe motion vector resolution indicated by the decoded resolutionidentification flag as the motion vector of the area. This configurationalso has been already described above in the discussion relating to theresolution change flag extractor 1810 of the video decoding apparatus1800 according to the first aspect, so a detailed description thereof isomitted here.

Further, when the resolution identification flag decoded for each areaor motion vector indicates the capability of estimation, the resolutiondecoder 4820 may reconstruct the motion vector resolution of thepertinent area or motion vector by additionally decoding the motionvector resolution in the resolution identification flag. Further, theresolution decoder 4820 can reconstruct the motion vector resolution ofeach area or motion vector only when each component of the differentialmotion vector is not “0”. That is, when a component of a differentialmotion vector of a particular area is “0”, the resolution decoder 4820may decode a predicted motion vector into a motion vector withoutreconstructing the motion vector resolution of the particular area. Thisconfiguration also has been already described above in the discussionrelating to the resolution change flag extractor 1810 of the videodecoding apparatus 1800 according to the first aspect, so a detaileddescription thereof is omitted here.

Further, the resolution decoder 4820 extracts a resolutionidentification flag according to the kind of the resolution of theresolution change flag decoded after being extracted from a header.Further, by using the extracted resolution identification flag, thedifferential vector decoder 4830 extracts a value of a differentialmotion vector corresponding to a pertinent resolution by referring to acode number extracted from a code number table of a differential motionvector according to the motion vector resolutions as shown in FIG. 25stored by a video encoding apparatus. When the decoded resolutionidentification flag is ¼, the motion vector may be decoded using adifferential motion vector extracted from a bitstream and a predictedmotion vector obtained through a conversion into the resolution (i.e. ¼)of surrounding motion vectors. The predicted motion vector may beobtained by taking a median of surrounding motion vectors convertedusing multiplication and division like the encoder, without limiting thepresent disclosure to this construction.

FIG. 49 illustrates an example of surrounding motion vectors of currentblock X, and FIG. 50 illustrates an example of converted values ofsurrounding motion vectors according to the current resolution.

Further, the resolution decoder 4820 may calculate the resolution byusing reference picture indexes without extracting a resolutionidentification flag. This configuration has been already described abovein the discussion relating to the video encoding apparatus 3200 withreference to FIGS. 30 and 31 , so a detailed description thereof isomitted here.

The inter prediction decoder 4840 may obtain and decode a motion vectorby using a differential motion vector calculated by the differentialvector decoder 4830 and a predicted motion vector obtained using a tableas shown in FIG. 50 .

When the differential motion vector resolution has been encoded and thentransmitted through a bitstream as described above with reference toFIGS. 26 and 27 , the resolution decoder 4820 extracts and decodes aresolution identification flag of a differential motion vector from thebitstream, and decodes a sign of a differential motion vector and a codenumber of the differential motion vector. When a code number extractedfrom a bitstream including a code number table of differential motionvectors according to the differential motion vector resolutions as shownin FIG. 27 is (1, 1), it is possible to obtain a differential motionvector of (−⅛, −¼) by referring to the code number extracted from abitstream including a code number table of differential motion vectorsaccording to the differential motion vector resolutions of FIG. 27 . Inthis event, the inter prediction decoder 4840 may calculate a predictedmotion vector in the same way as that of the video encoding apparatus asdescribed below.PMVx=median(⅞, ⅛, 2/8)= 2/8PMVy=median(− 6/8, ⅛, − 2/8)=− 2/8

As a result, PMV=( 2/8, − 2/8)=(¼, −¼).

Therefore, MV (⅛, − 4/8)=MVD(−⅛, −¼)−PMV(¼, −¼), so that (⅛, − 4/8) isobtained as the decoded motion vector.

Meanwhile, when the differential vector decoder 1830 receives areference resolution flag, the differential vector decoder 1830reconstructs a differential motion vector and decodes the referenceresolution. In this event, the differential vector decoder 1830 extractsa code number included in the reference resolution flag, decodes thedifferential reference motion vector by referring to the code numbertable according to the differential reference motion vector resolutionas shown in FIG. 29 , and then reconstructs the differential motionvector by using the location information included in the referenceresolution flag. That is, in decoding the differential motion vector,the differential vector decoder 1830 extracts a reference resolutionfrom a bitstream and calculates the differential reference motion vectorby referring to the code number table according to the differentialreference motion vector resolution as shown in FIG. 29 . In this event,the differential vector decoder 1830 may extract a reference resolutionflag, which indicates a reference resolution and location coordinates ofa motion vector, from a bitstream and then decode a differential motionvector from the extracted reference resolution flag by using thereference resolution flag.

If a motion vector has a resolution other than the reference resolution,it is possible to employ a method of additionally encoding a referenceresolution flag. The reference resolution flag may include dataindicating whether the motion vector has the same resolution as thereference resolution and data indicating a location of an actual motionvector.

Meanwhile, the differential vector decoder 4830 may have anotherfunction corresponding to the function of the differential vectordecoder 1830 of the video decoding apparatus 1800 according to the firstaspect as described above. This function has been already describedabove in the discussion relating to the differential vector decoder 1830according to the first aspect, so a detailed description thereof isomitted here.

According to the value (e.g. 1) of the resolution change flag extractedfrom a bitstream, a resolution identification flag is decoded afterbeing extracted from the bitstream by using the same resolutionidentification flag table as used in the encoder except for theresolution having the highest frequency among the surroundingresolutions.

Meanwhile, the resolution conversion flag extractor 4850 extracts aresolution conversion flag from a bitstream. Also, according to thevalue (e.g. 1) of the resolution change flag extracted from a bitstream,the resolution conversion flag extractor 4850 may decode a resolutionidentification flag after extracting the resolution identification flagfrom the bitstream by a resolution identification flag table (see thetable shown in FIG. 45 ) except for the resolution having the highestfrequency among the surrounding resolutions. Further, in the case ofusing the resolutions of surrounding blocks, the resolution conversionflag extractor 4850 may decode the resolution conversion flag into 0when the resolution of the current block is equal to the lowestresolution among the resolutions of A and B, and may decode theresolution conversion flag into 1 when the resolution of the currentblock is equal to the highest resolution. When the resolution conversionflag is encoded into 1, the encoded flag may be excluded from theresolution identification flag.

Meanwhile, the resolution conversion flag extractor 4850 may obtain theresolution of the current block by extracting the value (i.e. 1) of theresolution conversion flag from a bitstream so as to enable thedifference between the resolution of the current block and theresolution of previous block A to be understood. For example, when theresolution set includes ½ and ¼ and the resolution of the previous blockis ½, it is possible to understand that the converted resolution is ¼.

In the meantime, a video encoding apparatus/video decoding apparatusaccording to an aspect of the present disclosure can be implemented byconnecting a bitstream output port of the video encoding apparatus shownin FIG. 9 or 32 and a bitstream input port of the video decodingapparatus shown in FIG. 18 or 48 with each other.

A video encoding apparatus/video decoding apparatus according to anaspect of the present disclosure includes: a video encoder fordetermining a motion vector resolution of each area or motion vector andperforming an inter prediction encoding of a video in the unit of areasof the video by using a motion vector according to the motion vectorresolution determined for each area or motion vector; and a videodecoder for reconstructing a resolution by extracting resolutioninformation from a bitstream and then performing an inter predictiondecoding of each area of a video by using a motion vector according tothe motion vector resolution of each area or motion vector of the video.

FIG. 19 is a flowchart of a method for decoding a video by using anadaptive motion vector resolution according to the first aspect of thepresent disclosure.

In the method for decoding a video by using an adaptive motion vectorresolution according to the first aspect of the present disclosure, aresolution change flag is extracted from a bitstream, an encodedresolution identification flag is extracted from a bitstream accordingto the extracted resolution change flag and is then decoded so that amotion vector resolution of each area or motion vector is reconstructed,and an inter prediction decoding of each area is performed using amotion vector of each area according to the motion vector resolution ofeach area or motion vector.

To this end, the video decoding apparatus 1800 extracts a resolutionchange flag from a bitstream (step S1910), determines if the extractedresolution change flag indicates that the motion vector resolutionchanges according to each area or motion vector (step S1920),reconstructs a motion vector resolution of each area or motion vector byextracting a resolution identification flag from a bitstream anddecoding the extracted resolution identification flag when theresolution change flag indicates that the motion vector resolutionchanges according to each area or motion vector (step S1930), andreconstructs a motion vector of each area or motion vector by thereconstructed motion vector resolution and then performs an interprediction decoding of the reconstructed motion vector (step S1940).Further, when the resolution change flag indicates that the motionvector resolution does not change according to each area or motionvector but is fixed, the video decoding apparatus 1800 reconstructs amotion vector resolution by extracting the resolution identificationflag from a bitstream and decoding the extracted resolutionidentification flag (step S1950), and reconstructs a motion vectoraccording to the fixed motion vector resolution for lower areas definedin a header according to the reconstructed motion vector resolution andthen performs an inter prediction decoding of each area of thereconstructed motion vector (step S1960). In this event, the motionvector resolution decoded for each area or motion vector may havedifferent values for an x component and a y component of the motionvector.

The video decoding apparatus 1800 may reconstruct the motion vectorresolution of each area or motion vector by decoding a resolutionidentification flag hierarchically encoded in a Quadtree structure bygrouping areas having the same motion vector resolution together, mayreconstruct the motion vector resolution of each area by decoding aresolution identification flag hierarchically encoded using a motionvector resolution predicted using motion vector resolutions ofsurrounding areas of each area, may reconstruct the motion vectorresolution of each area or motion vector by decoding a resolutionidentification flag in which the run and length of a motion vectorresolution of each area or motion vector have been encoded, mayreconstruct the motion vector resolution of each area or motion vectorby decoding a resolution identification flag hierarchically encodedusing a tag tree, may reconstruct the motion vector resolution of eacharea or motion vector by decoding a resolution identification flag witha changing number of bits allocated to the resolution identificationflag according to the frequency of the motion vector resolution of eacharea or motion vector, may estimate a motion vector resolution accordingto a pre-promised estimation scheme and reconstruct the estimated motionvector resolution as a motion vector resolution of the correspondingarea or motion vector when the resolution identification flag decodedfor each area or motion vector corresponds to a flag indicating thecapability of estimation, or may reconstruct a motion vector resolutionindicated by the decoded resolution identification flag when theresolution identification flag decoded for each area or motion vectorcorresponds to a flag indicating the incapability of estimation. In thisevent, the video decoding apparatus 1800 may decode and reconstruct anidentifier, which indicates the size of an area indicated by the lowestnode of the Quadtree layers and the maximum number of the Quadtreelayers or the size of an area indicated by the lowest node of the tagtree layers and the maximum number of the tag tree layers, from a headerof a bitstream.

Further, the video decoding apparatus 1800 may extract and decode anencoded differential motion vector from a bitstream. In this event, thevideo decoding apparatus 1800 may decode and reconstruct a differentialmotion vector of each area or motion vector according to a motion vectorresolution of each reconstructed area or motion vector. Additionally,the video decoding apparatus 1800 may predict a predicted motion vectorof each area or motion vector and then reconstruct a motion vector ofeach area by using the reconstructed differential motion vector and thepredicted motion vector.

To this end, the video decoding apparatus 1800 may decode thedifferential vector by using the UVLC. In this event, the video decodingapparatus 1800 may use the K-th order Exp-Golomb code in the decoding,and may change the degree of order (K) of the Exp-Golomb code accordingto the motion vector resolution determined for each area. The videodecoding apparatus 1800 may decode the differential motion vector byusing a text-based binary arithmetic coding. In the decoding, the videodecoding apparatus 1800 may use the Concatenated Truncated Unary/K-thOrder Exp-Golomb Code and may change the degree of order (K) and themaximum value (T) of the Concatenated Truncated Unary/K-th OrderExp-Golomb Code according to the motion vector resolution of eachreconstructed area or motion vector. When the video decoding apparatus1800 decodes the differential vector by using the CABAC, the videodecoding apparatus 1800 may differently calculate the accumulationprobability according to the motion vector resolution of eachreconstructed area or motion vector.

Further, the video decoding apparatus 1800 may predict a predictedmotion vector for a motion vector of each area by using motion vectorsof surrounding areas of each area. In this event, when the motion vectorresolution of each area is not equal to the motion vector resolution ofsurrounding areas, the video decoding apparatus 1800 may perform theprediction after converting the motion vector resolution of thesurrounding areas to the motion vector resolution of said each area. Thepredicted motion vector may be obtained by the same method in the videoencoding apparatus and the video decoding apparatus. Therefore, variousaspects of deriving a predicted motion vector by a video encodingapparatus can be also implemented in a video decoding apparatusaccording to an aspect of the present disclosure.

In addition, the video decoding apparatus 1800 may use different methodsof decoding a resolution identification flag according to thedistribution of the motion vector resolutions of surrounding areas ofeach area with respect to the motion vector resolution determinedaccording to each area or motion vector.

Further, in performing the entropy decoding by an arithmetic decoding,the video decoding apparatus 1800 may use different methods ofgenerating a bit string of a resolution identification flag according tothe distribution of the motion vector resolutions of the surroundingareas of each area and may apply different context models according tothe distribution of the motion vector resolutions of the surroundingareas and the probabilities of the motion vector resolution havingoccurred up to the present, for the arithmetic decoding and probabilityupdate. Also, the video decoding apparatus 1800 may use differentcontext models according to the bit positions for the arithmeticdecoding and probability update.

Moreover, when one or more areas among the areas is a block and theblock mode of the block is a skip mode, the video decoding apparatus1800 may convert the motion vector resolution of the area of the motionvector to be predicted as the highest resolution among the motion vectorresolutions of surrounding areas of the area and then perform theprediction.

FIG. 51 is a flowchart illustrating a video decoding method using anadaptive motion vector resolution according to the second aspect of thepresent disclosure.

The video decoding method using an adaptive motion vector resolutionaccording to the second aspect of the present disclosure includes: aresolution appointment flag extracting step (S5102), a resolutiondecoding step (S5104), a differential vector decoding step (S5106), aninter prediction decoding step (S5108), and a resolution conversion flaggenerating step (S5110).

The resolution appointment flag extracting step (S5102) corresponds tothe operation of the resolution appointment flag extractor 4810, theresolution decoding step (S5104) corresponds to the operation of theresolution decoder 4820, the differential vector decoding step (S5106)corresponds to the operation of the differential vector decoder 4830,the inter prediction decoding step (S5108) corresponds to the operationof the inter prediction decoder 4840, and the resolution conversion flaggenerating step (S5110) corresponds to the operation of the resolutionconversion flag extractor 4850. Therefore, a detailed description oneach step is omitted here.

Meanwhile, a video encoding/decoding method according to an aspect ofthe present disclosure can be implemented by combining a video encodingmethod according to the first or second aspect and a video decodingmethod according to the first or second aspect of the presentdisclosure.

A video encoding/decoding method according to an aspect of the presentdisclosure includes: a video encoding step for determining a motionvector resolution of each area or motion vector and performing an interprediction encoding of a video in the unit of areas of the video byusing a motion vector according to the motion vector resolutiondetermined for each area or motion vector; and a video decoding step forreconstructing a resolution by extracting resolution information from abitstream and then performing an inter prediction decoding of each areaof a video by using a motion vector according to the motion vectorresolution of each area or motion vector of the video.

FIG. 52 is a block diagram illustrating a video encoding apparatus 5200using an adaptive motion vector according to the third aspect of thepresent disclosure.

A video encoding apparatus 5200 using an adaptive motion vectoraccording to the third aspect of the present disclosure includes aninter prediction encoder 3210, a resolution appointment flag generator3220, a resolution encoder 3240, a resolution conversion flag generator3260, a predicted motion vector calculator 5210, and a skip mode encoder5220. Meanwhile, it is not inevitably required that all of theresolution appointment flag generator 3220, resolution encoder 3240, andthe resolution conversion flag generator 3260 should be included in thevideo encoding apparatus 5200, and they may be selectively included inthe video encoding apparatus 5200.

The inter prediction encoder 3210 performs an inter prediction encodingof a video in the unit of areas of the image by using a motion vectoraccording to a motion vector resolution determined for each motionvector or each area of the video. The inter prediction encoder 3210 canbe implemented by the video encoding apparatus 100 described above withreference to FIG. 1 . In this event, when the resolution encoder 3240 ofFIG. 52 is additionally included and the function of the additionallyincluded resolution encoder 3240 overlaps with the function of theencoder 150 within the video encoding apparatus 5200, the overlappingfunction may be omitted in the encoder 150.

Further, the resolution encoder 3240 and the skip mode encoder 5220 maybe configured either as elements separate from the inter predictionencoder 3210 as shown in FIG. 52 or as an element integrally formed withthe encoder 150 within the inter prediction encoder 3210. Further, theflag information generated in the resolution appointment flag generator3220, the resolution encoder 3240, or the resolution conversion flaggenerator 3260 may be transformed into a bitstream either by theresolution appointment flag generator 3220, the resolution encoder 3240,or the resolution conversion flag generator 3260 or by the encoder 150within the inter prediction encoder 3210. Meanwhile, the operation ofthe predicted motion vector calculator 5210 may include the operation ofthe resolution determiner 3230. Further, the operations of the interprediction encoder 3210, the resolution appointment flag generator 3220,the resolution encoder 3240, and the resolution conversion flaggenerator 3260 may include the functions of the inter prediction encoder3210, the resolution appointment flag generator 3220, the resolutionencoder 3240, and the resolution conversion flag generator 3260 asdescribed above with reference to FIG. 32 , respectively.

Further, when the function of the predicted motion vector calculator5210 overlaps with the function of the predictor 110 within the interprediction encoder 3210, the overlapping function may be omitted in thepredictor 110. Further, the predicted motion vector calculator 5210 maybe configured either as an element separate from the inter predictionencoder 3210 as shown in FIG. 52 or as an element integrally formed withthe predictor 110 within the inter prediction encoder 3210.

Hereinafter, a description will be made with reference to FIG. 52 .

The predicted motion vector calculator 5210 calculates a predictedmotion vector of a current block to be encoded using motion vectors ofone or more surrounding blocks.

When a result of the prediction on the current block and the predictedmotion vector satisfy the skip condition, the skip mode encoder 5220encodes information indicating that the current block is a skip block.

The resolution encoder 3240 encodes information indicating a resolutionof a motion vector of the current block.

In this event, a resolution of at least one motion vector among themotion vectors of the surrounding blocks and the motion vector of thecurrent block may have a value different from values of resolutions ofthe other motion vectors.

The predicted motion vector calculator 5210 may convert the resolutionof a predicted motion vector or at least one motion vector among themotion vectors of the surrounding blocks.

The predicted motion vector calculator 5210 may convert the resolutionof the predicted motion vector or at least one motion vector among themotion vectors of the surrounding blocks to a resolution equal to apreset resolution of the current block.

The predicted motion vector calculator 5210 may convert one or moreresolutions among the resolutions of the motion vectors of thesurrounding blocks.

The predicted motion vector calculator 5210 may convert the resolutionof the predicted motion vector.

The predicted motion vector calculator 5210 may convert the resolutionsso as to make the motion vectors of the surrounding blocks have the sameresolution.

Meanwhile, the information indicating the resolution of the motionvector of the current block may indicate the resolution of the convertedpredicted motion vector.

Further, the information indicating the resolution of the motion vectorof the current block may indicate the same resolution of the surroundingblocks.

In the meantime, the inter prediction encoder 3210 may store a blockreferred to by the predicted motion vector as a block constructed byencoding the current block, so as to enable the current block to be usedas a reference picture.

FIG. 53 is a block diagram illustrating a video decoding apparatus usingan adaptive motion vector according to the third aspect of the presentdisclosure.

A video decoding apparatus 5300 using an adaptive motion vectoraccording to the third aspect of the present disclosure includes aresolution appointment flag extractor 4810, a resolution conversion flagextractor 4850, a skip information extractor 5310, a predicted motionvector calculator 5320, and a skip block decoder 5330. In this event, itis not required that both of the resolution appointment flag extractor4810 and the resolution conversion flag extractor 4850 should beincluded in the video decoding apparatus 5300, and they may beselectively included in the video decoding apparatus 5300 according tothe encoding scheme of a video encoding apparatus for generating anencoded bitstream. The operation of the predicted motion vectorcalculator 5320 may include the operation of the resolution decoder 4820of FIG. 48 . Further, the operations of the resolution appointment flagextractor 4810 and the resolution conversion flag extractor 4850 mayinclude the operations of the resolution appointment flag extractor 4810and the resolution conversion flag extractor 4850.

The skip information extractor 5310 decodes information indicating the acurrent block to be decoded is a skip block.

The predicted motion vector calculator 5320 obtains a predicted motionvector of the current block to be decoded using motion vectors of one ormore surrounding blocks.

The skip block decoder 5330 selects the predicted motion vector as themotion vector of the current block and then decodes the current blockinto the skip mode by using the motion vector of the current block.

In this event, a resolution of at least one motion vector among themotion vectors of the surrounding blocks and the motion vector of thecurrent block may have a value different from values of resolutions ofthe other motion vectors.

The predicted motion vector calculator 5320 may convert the resolutionof a predicted motion vector or at least one motion vector among themotion vectors of the surrounding blocks.

The predicted motion vector calculator 5320 may convert the resolutionof the predicted motion vector or at least one motion vector among themotion vectors of the surrounding blocks to the same resolution as aresolution predetermined as the resolution of the motion vector of theskip block.

The resolution decoder 4820 decodes information indicating a resolutionof a motion vector. In this event, the predicted motion vectorcalculator 5320 obtains a predicted motion vector of the current blockby using the information indicating resolutions of a motion vector andmotion vectors of one or more surrounding blocks.

The predicted motion vector calculator 5320 may convert one or moreresolutions among the resolutions of the motion vectors of thesurrounding blocks.

The predicted motion vector calculator 5320 may convert the resolutionof the predicted motion vector.

The predicted motion vector calculator 5320 may convert the resolutionsso as to make the motion vectors of the surrounding blocks have the sameresolution.

In this event, the information indicating the resolution of the motionvector of the current block may indicate the resolution of the convertedpredicted motion vector. Further, the information indicating theresolution of the motion vector of the current block may indicate thesame resolution of the surrounding blocks.

Hereinafter, an encoding and a decoding in a skip mode, to which anadaptive motion vector resolution according to the present disclosurehas been applied, will be described with reference to the video encodingapparatus and the video decoding apparatus as shown in FIGS. 52 and 53 .

The skip mode of the inter prediction can achieve a high efficiencyencoding by signaling non-existence of information, required fordecoding of the block to be decoded, within a bitstream to a videodecoding apparatus.

For example, in a case in which the skip mode encoder 5220 tries toencode the current block in order to determine whether the skipcondition is satisfied, if the motion vector of the current block isidentical to the predicted motion vector, the reference picture index is0, and it is determined that all quantized coefficients within thecurrent block obtained by converting and quantizing the obtainedresidual signal (this determination can be made based on the result fromthe quantizer 140), the skip mode encoder 5220 encodes informationindicating that the current block is a skip block, which implies thatthe current block can be decoded in the skip mode, and then transmitsthe encoded information to the video decoding apparatus 5300. Therefore,the skip mode implies that the motion vector of the current block isidentical to the predicted motion vector, the reference picture index is0, and there is no residual signal conversion coefficient data.Accordingly, at the time of encoding into the skip mode, it will do ifthe skip mode encoder 5220 encodes only the skip flag 1 bit.

In this event, the skip information extractor 5310 of the video decodingapparatus 5300 extracts a skip flag from a bitstream, and the predictedmotion vector calculator 5320 calculates a predicted motion vector asthe motion vector of the current block when the encoding mode of thecurrent block is a skip mode, that is to say, when the skip flagindicates the skip mode. In this event, since the residual signal of thecurrent block is 0, the skip block decoder 5330 uses the predicted blockobtained using the motion vector determined in the way described aboveas a reconstructed block (i.e. decoded block) of the current block. Theblock encoded in the skip mode as described above is called a skipblock.

Meanwhile, the present disclosure may use either a fixed value or anadaptively changing value as the resolution of the motion vector of theskip block. The resolution may be a resolution of a motion vector or aresolution of a predicted motion vector.

In the case of using a fixed motion vector resolution in encoding ordecoding in the skip mode, the predicted motion vector calculator 5210and the predicted motion vector calculator 5320 of a video encodingapparatus use the same resolution. Further, when the motion vectorresolution is fixed, a predetermined resolution may be selected. Forexample, the highest resolution may be selected from possibleresolutions. The predicted motion vector calculator 5210 of the videoencoding apparatus and the predicted motion vector calculator 5320 ofthe video decoding apparatus may calculate a predicted motion vector ofa skip block to be encoded or decoded using surrounding motion vectorsbased on a predetermined motion vector resolution. The predicted motionvector may be obtained by the same method in the predicted motion vectorcalculator 5210 of the video encoding apparatus and the predicted motionvector calculator 5320 of the video decoding apparatus. Therefore,various aspects of deriving the predicted motion vector as describedabove with reference to FIG. 22 and aspects relating to the motionvector resolution conversion as described above with reference to FIGS.23 and 24 may be also applied to the encoding or decoding of the skipblock described below.

If the motion vector resolution appointment flag appoints ½, ¼, and ⅛ asthe kinds of resolutions and the motion vector resolution of a skipblock is fixed to ⅛, the predicted motion vector calculator 5210 of thevideo encoding apparatus or the predicted motion vector calculator 5320of the video decoding apparatus may obtain a predicted motion vector ofthe skip block by converting the motion vector resolution of motionvectors of the surrounding blocks to ⅛ using the conversion formulashown in FIG. 23 and then calculating a median value thereof. Otherwise,the predicted motion vector calculator 5210 of the video encodingapparatus or the predicted motion vector calculator 5320 of the videodecoding apparatus may use a value, which is obtained by calculating amedian value of the surrounding motion vectors without converting theresolution of the surrounding motion vectors and then converting theresolution of the median value to ⅛, as the predicted motion vector ofthe skip block.

Otherwise, the predicted motion vector calculator 5210 of the videoencoding apparatus or the predicted motion vector calculator 5320 of thevideo decoding apparatus may use a median value of the surroundingmotion vectors without converting the resolution of the surroundingmotion vectors, as the predicted motion vector of the skip block.Otherwise, the predicted motion vector calculator 5210 of the videoencoding apparatus or the predicted motion vector calculator 5320 of thevideo decoding apparatus may obtain the predicted motion vector by usingonly the motion vector having a resolution of ⅛ among the surroundingmotion vectors. In this event, the skip mode encoder 5220 of the videoencoding apparatus encodes information (a skip mode flag) indicatingthat the current block has been encoded in the skip mode. The skipinformation extractor 5310 of the video decoding apparatus may extract askip mode flag from a bitstream. Then, when the skip mode flag indicatesthe skip mode, the predicted motion vector calculator 5320 obtains thepredicted motion vector and uses the predicted motion vector as themotion vector of the current block, like the predicted motion vectorcalculator 5210 of the video encoding apparatus.

Hereinafter, an aspect of adaptively selecting a motion vectorresolution of a skip block will be described.

In the case of adaptively selecting a motion vector resolution of a skipblock, the skip mode encoder 5220 according to the present disclosureencodes a skip mode flag, the resolution encoder 3240 encodes a motionvector resolution identification flag, and the resolution conversionflag generator 3260 encodes a motion vector resolution conversion flag.

The skip information extractor 5310 of the video decoding apparatus 5300extracts a skip mode flag from a bitstream, and the resolution decoder4820 and the resolution conversion flag extractor 4850 extract anddecode a motion vector resolution identification flag and a motionvector resolution conversion flag, respectively. In this event, thepredicted motion vector calculator 5320 may calculate the predictedmotion vector of the skip block by using the motion vector resolution ofthe decoded motion vector. The predicted motion vector may be obtainedby the same method as that of the predicted motion vector calculator5210. Therefore, various aspects of deriving the predicted motion vectoras described above with reference to FIG. 22 and aspects relating to themotion vector resolution conversion as described above with reference toFIGS. 23 and 24 may be also applied to the encoding or decodingaccording to the skip mode described below.

In the aspects described above, the motion vector of the current blockhas been determined, the resolution of the motion vector of surroundingblocks or the resolution of a predicted motion vector obtained usingmotion vectors of the surrounding blocks is converted to a resolutionequal to the determined resolution of the motion vector of the currentblock. However, in the case of the skip block, a motion vector of theskip block does not exist.

Therefore, the predicted motion vector calculator 5210 of the videoencoding apparatus 5200 according to an aspect of the present disclosureconverts the motion vectors of the surrounding blocks with respectivepossible resolutions, and calculates a predicted motion vector of eachresolution by using the converted motion vector resolutions of thesurrounding blocks according to the respective resolutions. Then, thepredicted motion vector calculator 5210 may select a motion vectorhaving the best encoding efficiency among the predicted motion vectorsobtained according to the resolutions as a motion vector of the skipblock, and then encode a resolution of the selected motion vector byusing the flags as described above.

The predicted motion vector calculator 5210 according to another aspectof the present disclosure obtains a predicted motion vector by usingmotion vectors of the surrounding blocks and then converts the predictedmotion vector according to each resolution. Then, the predicted motionvector calculator 5210 may select a motion vector having the bestencoding efficiency among the converted predicted motion vectorsaccording to the resolutions as a motion vector of the skip block, andthen encode a resolution of the selected motion vector by using theflags as described above.

If a motion vector resolution appointment flag appoints ½, ¼, and ⅛ asthe kinds of motion vector resolutions and the motion vector resolutionis encoded using the motion vector resolution identification flag, thepredicted motion vector of the skip block may be obtained by convertingthe resolutions of the surrounding motion vectors to the motion vectorresolution of the current skip mode and then taking a median thereof byusing the conversion formula shown in FIG. 23 . In this event, the skipmode encoder 5220 may encode the skip mode flag and encode the optimumresolution of the skip mode by using the resolution identification flag.

In this event, the skip information extractor 5310 of the video decodingapparatus 5300 extracts a skip flag from a bitstream. Then, when theencoding mode of the current block is a skip mode, the predicted motionvector calculator 5320 obtains a median value by decoding the motionvector resolution identification flag and converting the surroundingmotion vectors according to a corresponding motion vector resolution,and then uses the median value as a predicted motion vector. Thispredicted motion vector is used as the motion vector of the skip block.

Further, the resolution of the motion vector may be indicated using themotion vector resolution conversion flag extracted by the resolutionconversion flag extractor 4850 and the motion vector resolutionidentification flag extracted by the predicted motion vector calculator5320. In this event, the motion vector resolution conversion flag mayindicate whether a resolution conversion from the motion vectorresolution of the previously encoded skip mode has been performed ornot. Otherwise, the motion vector resolution conversion flag mayindicate whether a resolution conversion from the motion vectorresolution of the previous block has been performed or not.

If a motion vector resolution appointment flag extracted by theresolution appointment flag extractor 4810 appoints ¼ and ⅛ as the kindsof motion vector resolutions and the motion vector resolution is encodedusing the motion vector resolution conversion flag, it is not necessaryto encode the motion vector resolution identification flag. In thisevent, from the motion vector resolution conversion flag, the videodecoding apparatus can determine whether the resolution is equal to themotion vector resolution of the previously decoded block or thepreviously decoded skip mode.

Further, the resolution identification flag, the resolution appointmentflag, and the resolution conversion flag may indicate a resolution of apredicted motion vector. In this event, the predicted motion vector canbe calculated using a selected predicted motion vector resolution. Thepredicted motion vector can be obtained in the same way in the videoencoding apparatus and in the video decoding apparatus. Therefore,various aspects of deriving the predicted motion vector and aspectsrelating to the motion vector resolution conversion as described abovewith reference to FIGS. 22 to 26 may be also applied to the encoding ordecoding of the skip block described below.

If the predicted motion vector resolution appointment flag appoints ½,¼, and ⅛ as the kinds of predicted motion vector resolutions and encodesthe resolution of the predicted motion vector by using the predictedmotion vector resolution identification flag, the predicted motionvector may be calculated by converting the resolutions of thesurrounding motion vectors according to the predicted motion vectorresolution. Further, the predicted motion vector may be calculated usingsurrounding motion vectors having the same resolution as the predictedmotion vector resolution.

In the meantime, a video encoding apparatus/video decoding apparatusaccording to an aspect of the present disclosure can be implemented byconnecting a bitstream output port of the video encoding apparatus shownin FIG. 9, 32 , or 52 and a bitstream input port of the video decodingapparatus shown in FIG. 18, 48 , or 53 with each other.

An apparatus for encoding/decoding a video according to an aspect of thepresent disclosure includes: a video encoder for calculating a predictedmotion vector of a current block to be encoded using motion vectors ofone or more surrounding blocks, and encoding a result of prediction ofthe current block and information indicating that the current block is askip block when the predicted motion vector satisfies a skip condition;and a video decoder for decoding information indicating that a currentblock to be decoded is a skip block, calculating a predicted motionvector of the current block to be decoded using motion vectors of one ormore surrounding blocks, selecting the calculated predicted motionvector as a motion vector of the current block to be decoded, anddecoding the current block in the skip mode by using the motion vectorof the current block.

A video encoding method according to the third aspect of the presentdisclosure includes a predicted motion vector calculating step (S5402)for calculating a predicted motion vector of a current block to beencoded using motion vectors of one or more surrounding blocks and askip mode encoding step (S5404) for encoding a result of prediction ofthe current block and information indicating that the current block is askip block when the predicted motion vector satisfies a skip condition.

The predicted motion vector calculating step (S5402) corresponds to theoperation of the predicted motion vector calculator 5210 and the skipmode encoding step (S5404) corresponds to the operation of the skip modeencoder 5220, so a more detailed description thereof is omitted here.

A video decoding method according to the fourth aspect of the presentdisclosure includes a predicted motion vector calculating step (S5502)for calculating a predicted motion vector of a current block to beencoded using motion vectors of one or more surrounding blocks, a skipmode encoding step (S5504) for encoding a result of prediction of thecurrent block and information indicating that the current block is askip block when the predicted motion vector satisfies a skip condition,and a resolution encoding step (S5506) for encoding informationindicating a resolution of the motion vector of the current block.

The predicted motion vector calculating step (S5502) corresponds to theoperation of the predicted motion vector calculator 5210, the skip modeencoding step (S5504) corresponds to the operation of the skip modeencoder 5220, and the resolution encoding step (S5506) corresponds tothe operation of the resolution encoder 3240, so a more detaileddescription thereof is omitted here.

A video decoding method according to the third aspect of the presentdisclosure includes a skip information extracting step (S5602) fordecoding information indicating that a current block to be decoded is askip block, a predicted motion vector calculating step (S5604) forcalculating a predicted motion vector of the current block to be decodedusing motion vectors of one or more surrounding blocks, and a skip blockdecoding step (S5606) for selecting the calculated predicted motionvector as a motion vector of the current block to be decoded anddecoding the current block in the skip mode by using the motion vectorof the current block.

The skip information extracting step (S5602) corresponds to theoperation of the skip information extractor 5310, the predicted motionvector calculating step (S5604) corresponds to the operation of thepredicted motion vector calculator 5320, and the skip block decodingstep (S5606) corresponds to the operation of the skip block decoder5330, so a more detailed description thereof is omitted here.

A video decoding method according to the fourth aspect of the presentdisclosure includes a skip information extracting step (S5702) fordecoding information indicating that a current block to be decoded is askip block, a resolution decoding step (S5704) for decoding informationindicating a resolution of a motion vector, a predicted motion vectorcalculating step (S5706) for calculating a predicted motion vector ofthe current block to be decoded using motion vectors of one or moresurrounding blocks, and a skip block decoding step (S5708) for selectingthe calculated predicted motion vector as a motion vector of the currentblock to be decoded and decoding the current block in the skip mode byusing the motion vector of the current block.

The skip information extracting step (S5702) corresponds to theoperation of the skip information extractor 5310, the resolutiondecoding step (S5704) and the predicted motion vector calculating step(S5706) correspond to the operation of the predicted motion vectorcalculator 5320, and the skip block decoding step (S5708) corresponds tothe operation of the skip block decoder 5330, so a more detaileddescription thereof is omitted here.

Meanwhile, a video encoding/decoding method according to an aspect ofthe present disclosure can be implemented by combining one of videoencoding methods according to the first to fourth aspects of the presentdisclosure and one of video decoding methods according to the first tofourth aspects of the present disclosure.

A method for encoding/decoding a video according to an aspect of thepresent disclosure includes: a video encoding step of calculating apredicted motion vector of a current block to be encoded by using motionvectors of one or more surrounding blocks, and encoding a result ofperforming a prediction of the current block and information indicatingthat the current block is a skip block when the predicted motion vectorsatisfies a skip condition; and a video decoding step of decodinginformation indicating that a current block to be decoded is a skipblock, calculating a predicted motion vector of the current block to bedecoded using motion vectors of one or more surrounding blocks,selecting the calculated predicted motion vector as a motion vector ofthe current block to be decoded, and decoding the current block in theskip mode by using the motion vector of the current block.

As described above, according to aspects of the present disclosure, itis possible to determine a motion vector resolution may be determined inthe unit of motion vector or area having a predetermined size of a videoaccording to the characteristics of the video (e.g. the degree ofcomplexity or the degree of movement of the video) and to perform aninter prediction encoding by using a motion vector having an adaptivemotion vector resolution. Therefore, the present disclosure can improvethe quality of the video while reducing the quantity of bits involved inthe encoding, so as to enhance the compression efficiency. For example,an area (i.e. first area) in a certain picture of a video may have ahigh complexity and a small degree of movement while another area (i.e.second area) in the certain picture of the video may have a lowcomplexity and a large degree of movement. In this event, for the firstarea, an inter prediction encoding may be performed after enhancing themotion vector resolution of the first area, so as to increase theexactness of the inter prediction, which can reduce residual signals andthe quantity of encoded bits. Moreover, due to the small degree ofmovement of the first area, even the increase of the resolution in thefirst area does not greatly increase the quantity of bits, which canimprove the video quality while reducing the encoded bit quantity.Further, in relation to the second area, even an inter predictionencoding with a lower motion vector resolution does not greatly degradethe video quality of the second area, and the second area can allow alow motion vector resolution, which can increase the quantity of encodedbits of the motion vector. As a result, without substantially degradingthe video quality of the second area, the entire quantity of encodedbits can be reduced, which can improve the compression efficiency.

In the description above, although all of the components of the aspectsof the present disclosure may have been explained as assembled oroperatively connected as a unit, the present disclosure is not intendedto limit itself to such aspects. Rather, within the objective scope ofthe present disclosure, the respective components may be selectively andoperatively combined in any numbers. Every one of the components may bealso implemented by itself in hardware while the respective ones can becombined in part or as a whole selectively and implemented in a computerprogram having program modules for executing functions of the hardwareequivalents. Codes or code segments to constitute such a program may beeasily deduced by a person skilled in the art. The computer program maybe stored in computer readable media, which in operation can realize theaspects of the present disclosure. As the computer readable media, thecandidates include magnetic recording media, optical recording media,and carrier wave media.

In addition, terms like ‘include’, ‘comprise’, and ‘have’ should beinterpreted in default as inclusive or open rather than exclusive orclosed unless expressly defined to the contrary. All the terms that aretechnical, scientific or otherwise agree with the meanings as understoodby a person skilled in the art unless defined to the contrary. Commonterms as found in dictionaries should be interpreted in the context ofthe related technical writings not too ideally or impractically unlessthe present disclosure expressly defines them so.

Although exemplary aspects of the present disclosure have been describedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from essential characteristics of the disclosure. Therefore,exemplary aspects of the present disclosure have not been described forlimiting purposes.

Accordingly, the scope of the disclosure is not to be limited by theabove aspects but by the claims and the equivalents thereof.

INDUSTRIAL APPLICABILITY

As described above, the present disclosure is highly useful forapplication in the fields of compressing a video, performing an interprediction encoding by adaptively changing a motion vector resolution inthe unit of predetermined area, and thereby efficiently encoding avideo.

The invention claimed is:
 1. A video decoding apparatus for decodingblocks which are split from a picture to be decoded by adaptivelydetermining a motion vector resolution in the unit of blocks, theapparatus comprising: a decoder configured to decode, from a bitstream,a differential motion vector, and motion vector resolutionidentification information dedicated to a current block to be decodedamong the blocks split from the picture, wherein the differential motionvector is a difference between a current motion vector of the currentblock and a predicted motion vector for the current motion vector, andthe motion vector resolution identification information is used fordetermining a motion vector resolution of the differential motion vectoramong a plurality of motion vector resolutions; and an inter predictorconfigured to derive at least one predicted motion vector candidate frommotion vectors of one or more neighboring blocks of the current block,convert the predicted motion vector candidate such that the convertedpredicted motion vector candidate has the same motion vector resolutionas the motion vector resolution determined by the motion vectorresolution identification information, derive the predicted motionvector for the current motion vector from the converted predicted motionvector candidate, reconstruct the current motion vector of the currentblock, by adding the differential motion vector to the predicted motionvector, and predict the current block from a reference picture using thecurrent motion vector.
 2. The apparatus of claim 1, wherein the decoderis configured to decode resolution change information from thebitstream, wherein the motion vector resolution identificationinformation is decoded from the bitstream, when the resolution changeinformation represents that a motion vector resolution is adaptivelydetermined in units of blocks split from the picture.
 3. The apparatusof claim 1, wherein the resolution change information is decoded from aheader of the bitstream, the header being a sequence parameter set or apicture parameter set or a slice header.
 4. A video encoding method forencoding blocks, which are split from a picture to be encoded, by usingan adaptive motion vector resolution in the unit of blocks, theapparatus comprising: determining a current motion vector of a currentblock to be encoded among the blocks split from the picture, andpredicting the current block from a reference picture using the currentmotion vector; and encoding, into a bitstream, a differential motionvector, motion vector resolution identification information which arededicated to the current block, and residual signals corresponding todifferences between pixels in the current block and pixels in thepredicted block, wherein the motion vector resolution identificationinformation is used for determining a motion vector resolution of thedifferential motion vector among a plurality of motion vectorresolutions, wherein the encoding of the differential motion vectorcomprises: deriving at least one predicted motion vector candidate frommotion vectors of one or more neighboring blocks of the current block,converting the predicted motion vector candidate such that the convertedpredicted motion vector candidate has the same motion vector resolutionas the motion vector resolution determined by the motion vectorresolution identification information, deriving a predicted motionvector for the current motion vector from the converted predicted motionvector candidate, and generating the differential motion vector bysubtracting the predicted motion vector from the current motion vector.5. The method of claim 4, wherein resolution change information isfurther encoded into the bitstream, wherein the motion vector resolutionidentification information is encoded into the bitstream, when theresolution change information represents that a motion vector resolutionis adaptively determined in units of blocks.
 6. The method of claim 4,wherein the resolution change information is encoded in a header of thebitstream, the header being a sequence parameter set or a pictureparameter set or a slice header.
 7. A non-transitory recording mediumstoring a bitstream generated by a video encoding method for encodingblocks, which are split from a picture to be encoded, by using anadaptive motion vector resolution in the unit of blocks, the methodcomprising: determining a current motion vector of a current block to beencoded among the blocks split from the picture, and predicting thecurrent block from a reference picture using the current motion vector;and encoding, into a bitstream, a differential motion vector, motionvector resolution identification information which are dedicated to thecurrent block, and residual signals corresponding to differences betweenpixels in the current block and pixels in the predicted block, whereinthe motion vector resolution identification information is used fordetermining a motion vector resolution of the differential motion vectoramong a plurality of motion vector resolutions, wherein the encoding ofthe differential motion vector comprises: deriving at least onepredicted motion vector candidate from motion vectors of one or moreneighboring blocks of the current block, converting the predicted motionvector candidate such that the converted predicted motion vectorcandidate has the same motion vector resolution as the motion vectorresolution determined by the motion vector resolution identificationinformation, deriving a predicted motion vector for the current motionvector from the converted predicted motion vector candidate, andgenerating the differential motion vector by subtracting the predictedmotion vector from the current motion vector.